3 FORCE AND PRESSURE
I.
Tick (3) the most appropriate answer.
1. Force has :
(a) only magnitude
(b) only direction
(c) both magnitude and direction
(d) neither magnitude nor direction
2. The SI unit of force is :
(c) newton
(d) pascal
(a) joule
(b) kg/m2
3. A box of weight 400 N is kept on the floor. The area of contact
is 4 m2. The pressure exerted by the box on the floor is :
(a) 100 Pa
(b) 200 Pa
(c) 300 Pa
(d) 400 Pa
4. Friction :
(a) produces heat
(b) causes wear and tear
(c) opposes motion
(d) all of these
5. Wheel is made circular, because :
(a) it minimises friction
(b) it increases friction
(c) to make them attractive (d) none of these
6. A cricketer catches a ball. The force coming in action is :
(a) contact force
(b) gravitational force
(c) frictional force
(d) all of these
7. The unit of pressure is :
(a) joule
(b) newton
(c) pascal (d) none of these
8. To increase pressure :
(a) area of contact is increased
(b) area of contact is decreased
(c) magnitude of thrust is decreased
(d) none of these
9. A boy is pulling a cart by a force of 100 N. The frictional force
experienced by the cart is 20 N. The force that causing the
motion of the cart is :
(a) 100 N
(b) 120 N
(c) 80 N
(d) 5 N
Class-VI Physics
1
Question Bank
10. Tyres are provided with deep grooves on their surface to :
(a) reduce the cost of material used
(b) increase the friction
(c) decrease the friction
(d) make them attractive
11. Gravitational force is a :
(a) contact force
(b) consequential force
(c) action-at-a-distance force (d) none of these
12. Friction is :
(a) always a disadvantage
(b) always an advantage
(c) sometimes a disadvantage and sometimes an advantage
(d) neither an advantage nor a disadvantage
13. Rockets have a special streamlined body in order to :
(a) increase friction
(b) reduce friction
(c) make them attractive
(d) none of these
14. The force which an object exerts on any other object is :
(a) gravitational force
(b) magnetic force
(c) electrostatic force
(d) frictional force
15. Burning of a meteor in the atmosphere is due to :
(a) electrostatic force
(b) magnetic force
(c) frictional force
(d) gravitational force
16. A stone falling from the roof of a house is an example of :
(a) frictional force
(b) magnetic force
(c) gravitational force
(d) electrostatic force
17. If area of contact is increased, then :
(a) pressure increases
(b) pressure decreases
(c) pressure remains constant (d) none of these
18. With the increase in the weight of an object the pressure :
(a) increases
(b) decreases
(c) remains unchanged
(d) none of these
19. One pascal is the pressure generated by :
(a) force of 1 N on 1 m2
(b) force of 1 kgf on 1 m2
(c) force of 1 N on 1000 cm 2 (d) force of 1 N on 1 cm2
2
Class-VI Physics
2
Question Bank
20. The magnetic force is a :
(a) contact force
(b) force at distance
(c) consequential force
(d) none of these
21. Magnetic force causes :
(a) attraction only
(b) repulsion only
(c) both attraction and repulsion
(d) none of these
22. The deep grooves in the tyre of a tractor :
(a) decrease friction
(b) increase friction
(c) make it stable
(d) make tyre more attractive
23. The force of friction :
(a) increases with the weight of body
(b) decreases with the weight of body
(c) is not affected by the weight of body
(d) none of these
Ans. 1. (c) 2. (c) 3. (a) 4. (d) 5. (a) 6. (d) 7. (c) 8. (b) 9. (c)
10. (b) 11. (c) 12. (c) 13. (b) 14. (a) 15. (c) 16. (c) 17. (b)
18. (a) 19. (a) 20. (b) 21. (c) 22. (b) 23. (a).
II. Fill in the blanks :
1. The ratio between the _______ and _______ is called
pressure.
2. When a force of one _______ acts on an area of cross-section
1 m2, the pressure exerted is said to be one _______ .
3. The cutting edge of cutting instruments is sharpened because,
by _______ the area of cross-section, the _______ increases.
4. The broad tyres of a tractor _______ pressure on the soft
ground, and hence, prevent it from _______ in the ground.
5. With the increase in force, the magnitude of pressure on a given
area _______ .
6. Force is an external agent which _______ or tends to change
the state of rest or uniform _______ of a body.
7. The force of _______ always attracts objects towards the
earth.
Class-VI Physics
3
Question Bank
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
The force of _______ attracts tiny bits of paper.
_______ force can pull small objects of iron.
_______ force always opposes motion of body.
The SI unit of force is _______ .
Thrust is _______ force.
Force per unit _______ is called the _______ .
Gravitational force is always _______ in nature.
The SI unit of pressure is _______ .
If the area of contact is increased, then pressure _______ .
A stone falling from the roof of a house is an example of
_______ force.
18. Lubricants are used in machine to _______ friction.
19. A spring balance is used to measure _______ .
20. The force which opposes the motion is called _______ .
21. Force can change the _______ of motion of an object.
22. A charged comb attracts small pieces of paper due to _______
force.
23. The total force acting on a given surface is called the _______ .
24. Pressure is directly proportional to the _______ .
25. The army tanks move over _______ rather than wheels.
26. Oil is applied to machines to _______ friction.
27. _______ force is a force which is the outcome or resultant
when a force is applied on an object.
28. Muscular force is an example of _______ force.
Ans. 1. force, area of cross-section 2. newton, pascal 3. reducing,
pressure 4. reduce, sinking 5. increases 6. changes, motion
7. gravitation 8. electrostatic 9. magnetic 10. frictional 11. newton
12. normal upward 13. area, pressure 14. attractive 15. Pascal
16. decreases 17. gravitational 18. reduce 19. weight 20. friction
21. direction 22. electrostatic 23. pressure 24. thrust (force)
25. broad chain 26. reduce 27. consequential 28. contact.
4
Class-VI Physics
4
Question Bank
III. State whether the following statements are true or false (T/F):
1. The force required to lift a mass of 1 kg vertically upward is
called kgf.
2. A boy holding a suitcase in his hand is exerting no force.
3. A physical balance measures weight, but a spring balance
measures mass.
4. When a spaceship rises up from ground, no gravitational force
acts on it.
5. A boy standing on one leg exerts more pressure on ground than
a boy standing on two legs.
6. When a diver jumps in water, it is the force of friction which
slows his motion.
7. Long skies used by skiers to reduce the pressure on snow.
8. The broad side on thumb tack increases the pressure on the
thumb.
9. A blunt nail easily penetrates in wood than sharp nail.
10. The edge of knife is sharpened to increase the pressure.
11. Foundations of high rise building are small.
12. Army tanks move over a broad chain, because chain increases
the pressure on the ground.
Ans. 1. T 2. F 3. F 4. F 5. T 6. T 7. T 8. F 9. F 10. T 11. F 12. F.
IV. Statements given below are incorrect. Write the correct
statements.
1. When we walk on the ground the friction acts along the
direction of motion.
Ans. When we walk on the ground the friction acts opposite to the
direction of motion.
2. Air offers no friction.
Ans. Air offers friction.
3. Rolling friction is greater than sliding friction.
Ans. Rolling friction is much less than the sliding friction.
4. Elephants damage the ground more than that of Goats.
Ans. Goats damage the ground more than that of Elephants.
5. Pressure does not depend on area of contact.
Ans. Pressure depends on the area of contact.
Class-VI Physics
5
Question Bank
6. A leaf falling from a tree is an example of mechanical force.
Ans. A leaf falling from a tree is an example of gravitational force.
7. Weight of a man increases six times on moon’s surface.
1
th on moon’s surface.
6
Pressure is force per unit volume.
Pressure is force per unit area.
Powder applied on a carrom board increases friction.
Powder applied on a carrom board reduces friction.
Pressure is inversely proportional to the thrust.
Pressure is directly proportional to the thrust.
By sharpening a knife we decrease its surface area and hence
decrease pressure.
By sharpening a knife we decrease its surface area and hence
increase pressure.
Force of push can act through non-rigid connector.
Force of push can act through rigid connector.
The force which acts on a body directly or through a connector
is called consequential force.
The force which acts on a body directly or through a connector
is called contact force.
The force due to gravity is an example of contact force.
The force due to gravity is an example of force at distance.
The force of friction is an example of force at distance.
The force of friction is an example of consequential force.
The gravitational force always causes repulsion.
The gravitational force always causes attraction.
The magnetic force always causes attraction.
The magnetic force causes both attraction and repulsion.
Thrust per unit volume is called pressure.
Thrust per unit area is called pressure.
One pascal is the pressure produced by a force of 1 kgf on
a surface of 1 m2.
Ans. Weight of a man decreases to
8.
Ans.
9.
Ans.
10.
Ans.
11.
Ans.
12.
Ans.
13.
Ans.
14.
Ans.
15.
Ans.
16.
Ans.
17.
Ans.
18.
Ans.
19.
6
Class-VI Physics
6
Question Bank
Ans. One pascal is the pressure produced by a force of 1 N on a
surface of 1 m2.
20. Pressure increases with the increase in surface area.
Ans. Pressure decreases with the increase in surface area.
21. Pressure decreases with the increase in the weight of an object.
Ans. Pressure increases with the increase in the weight of an object.
22. The SI unit of pressure is newton.
Ans. The SI unit of pressure is pascal.
V. Match the following.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Column A
Column B
Moon revolves around the (a) Mechanical force
earth.
Iron nails are attracted by (b) Muscular force
A man lifts a weight.
(c) Gravitational force
Crane is used to lift a
(d) Magnetic force
heavy load.
Balloons move away from (e) Frictional force
each other after they are
rubbed against polyester
cloth.
A man walks on a levelled (f) Electrostatic force
road.
Applying the brakes of a
(g) Force changes the direction
bicycle to bring it to rest.
of a moving body.
Turning the handle-bar of
(h) Force increases the speed of
a bicycle at crossroads.
a moving body.
Applying the brakes of a
(i) Force decreases the speed of
cycle in a crowded street.
a moving body.
Pedalling towards the
(j) Force stops the motion of a
finishing line in a cycle
body.
race.
Stepping on to the pedal
(k) force starts the motion of a
of a standing bicycle.
body.
Class-VI Physics
7
Question Bank
Ans. 1. (c) 2. (d) 3. (b) 4. (a) 5. (f) 6. (e) 7. (j) 8. (g) 9. (i)
10. (h) 11. (k)
VI. With proper reasoning choose the odd one out:
1. Push, pull, pressure.
Ans. Pressure. As Push or pull is a force and pressure is force per
unit area.
2. Magnetic force, electric force, frictional force, gravitational
force.
Ans. Frictional force: Only frictional force is contact force and other
are action at a distance force.
3. A worker pulling a cart, a batsman hitting a cricket ball, a leaf
falling from a tree, lifting a bucket.
Ans. A leaf falling from a tree: Only a leaf falling from a tree does
not use muscular force but other use muscular force.
4. Rocket, racing car, boat, rickshaw.
Ans. Rocket: Only rocket moves against the gravitational pull of the
earth.
5. Using lubricants, using ball-bearings, polishing the surfaces,
making grooves in tyres.
Ans. Making groves in tyres. Making grooves in tyres increases the
friction but other are for reducing friction.
6. Tree, hut, earth, dustbin, chair.
Ans. Earth: Only earth can produce gravitational force.
7. Apple falling from a tree, car moving on a straight road, coins
moving over a carrom board.
Ans. Apple falling from a tree: Only apple falling from a tree is due
to gravitational force.
8. Kicking a football, lifting a school bag, meteors crossing the
atmosphere, horse pulling a cart.
Ans. Meteors crossing the atmosphere: It is due to the gravitational
force of earth but other are due to muscular force
9. Aeroplane, bird, lion, fish, submarine.
Ans. Lion: As lion does not have streamline body.
8
Class-VI Physics
8
Question Bank
10. Muscular force, mechanical force, gravitational force, frictional
force.
Ans. Gravitational force: Only gravitational force is action at a
distance force other are contact force.
11. Submarine, a flying bird, a cow, a rocket.
Ans. A cow: All other have streamline body except a cow.
VII. Differentiate between the following:
1. Contact force and consequential force.
Ans. Contact forces are the forces which act only when objects are
in physical contact with each other and bring about changes e.g.
muscular force mechanical force etc.
Consequential force is a force which is the outcome or resultant
when a force is applied on an object e.g. force of friction.
2. Force and pressure.
Ans. Force is a push or pull which changes or tends to change the
state of rest or of uniform motion or direction of motion.
And pressure is the force acting per unit area.
3. Tyres having grooves and fishes having streamlined bodies.
Ans. Tyres having grooves increases the friction with the surface of
road so that it will not slip.
Fishes having streamlined bodies reduce the force of friction in
water and help them to move faster.
4. Muscular force and gravitational force.
Ans. Muscular force is the force produced by the muscles of living
beings.
Gravitational force is the force or pull exerted by the earth on
the object.
5. Frictional force and gravitational force.
Ans. Frictional force is the force which acts at the surface of contact,
when one body moves upon another body.
Gravitational force is the force or pull exerted by the earth on
the object.
Class-VI Physics
9
Question Bank
6. Force and thrust.
Ans. Force is defined as push or pull.
Thrust is the total force acting normally on a given surface.
7. Electrostatic force and muscular force.
Ans. Electric force is the force exerted by electrostatic charge. It is
action at a distance force.
Muscular force is the force produced by the muscles of living
beings. It is contact force.
8. Sliding and rolling friction.
Ans. Sliding friction is the opposing force produced when one body
slides over another body in contact.
Rolling friction is the opposing force produced when one body
rolls over another body in contact.
VIII. Give reasons for the following.
1. Sparks are produced when a pair of scissors is sharpened
against a grinding wheel.
Ans. Due to the force of friction, sparks are produced when a pair
of scissors is sharpened against a grinding wheel.
2. A piece of chalk wears out as it is used on a blackboard.
Ans. A piece of chalk wears out due to the force of friction between
chalk and blackboard.
3. Oil is applied to the moving parts of a machine.
Ans. Oil is applied to the moving parts of a machine to reduce the
friction.
4. Powder is applied to a carrom board.
Ans. To reduce the friction powder is applied to a carrom board.
5. A man walking on the street slips on a banana skin.
Ans. A man walking on the street slips on a banana skin due to the
less friction between the banana skin and road.
6. The tyres of cars are made rough.
Ans. The tyres of cars are made rough to increase the friction with
the road and prevent tyres from slipping on wet or oily roads.
Class-VI Physics
10
10
Question Bank
7. Hover craft (a vessel which floats or a cushion of air) travels
faster than a steamer.
Ans. As hover craft is lighter than that of steamer, it produces less
pressure, so hover craft travels faster than a steamer.
8. The base of taller buildings are made broader.
Ans. The base of taller buildings are made broader because it
reduces the pressure exerted on the ground so that they do not
sink in due to the extremely high pressure of the building.
9. Trucks and buses generally have double wheels at the back.
Ans. Trucks and buses generally have double wheels at the back to
increase the area of contact on which their weights acts and
hence reduces the pressure on the ground.
10. Sand is spread on slippery road before working over it.
Ans. To increase the friction, so that people do not slip, sand is
spread on slippery road before working over it.
11. Wheels of a car are made circular.
Ans. Wheels of a car are made circular to reduce the friction between
the surface of the road and that of tyre, as rolling friction is
much less than the sliding friction.
12. Ball bearings are used in some machines.
Ans. Ball bearings are used in some machines to reduce the friction,
so the metal surface can move smoothly over one another
because of balls.
IX. Define the following terms.
1. Action-at-a-distance force 2. Consequential force 3. Muscular
force 4. Gravitational force 5. Force 6. Contact force 7. Friction
8. Thrust 9. Pressure
Ans. 1. Action-at-a-distance force: The forces which do not involve
physical contact between two bodies on which they act but they
act through the space between them is called action-at-adistance force.
2. Consequential force: It is a force which is the outcome or
resultant when a force is applied on an object.
Class-VI Physics
11
Question Bank
3. Muscular force: It is the force applied by the muscles.
4. Gravitational force: It is the force of attraction exerted by the
earth on all the objects.
5. Force: It is defined as push or pull.
6. Contact force: The forces which act on a body directly or
through a connector are called contact force.
7. Friction: An opposing force which acts at the surfaces of
contact when one body moves upon another body is called
force of friction.
8. Thrust: The total force acting normally on a surface is called
thrust.
9. Pressure: Pressure is the thrust acting per unit area i.e. P = .
X.
Answers these questions.
1. (a) Name two effects a force can have on a moving body.
(b) What do you understand by the term force?
(c) Name two effects a force can have on a stationary body.
Ans. (a) Two effects a force can have on a moving body are
(i) a force can stop the moving objects, and
(ii) a force can change the direction of moving objects.
(b) Force is an external agent which changes or tends to
change the state of rest or uniform motion of a body or
changes its direction or shape and size.
(c) Two effects a force can have on a stationary body are,
(i) a force can cause a motion in stationary objects
(ii) a force can change the shape of stationary object.
2. Name the type of force which acts in each of the following
cases:
(a) A cricket ball rolling down a cricket field.
(b) A stone falling downward.
(c) A bullock ploughing a field.
(d) A woodcutter cutting a tree.
(e) A plastic ruler on being moved through dry hair, is brought
near dry pieces of straw.
Class-VI Physics
12
12
Question Bank
Ans.
3.
Ans.
4.
Ans.
5.
(f) Fast moving wind driving a windmill.
(g) Falling of rain drops.
(h) Attraction of common pins towards magnet.
(i) Closing of door.
(j) A horse pulling a cart.
(a) frictional force
(b) gravitational force
(c) muscular force
(d) muscular force
(e) electrostatic force
(f) mechanical force
(g) gravitational force
(h) magnetic force
(i) muscular force
(j) muscular force
What do you understand by the
(a) contact forces,
(b) forces at a distance,
(c) consequential forces?
Support your answer with examples.
(a) Contact force: All forces which act on a body directly or
through a connector, are called contact forces e.g.
muscular force.
(b) Forces at a distance: The forces which do not make
direct contact with a body but act through space are called
forces at a distance, e.g. force of gravitation.
(c) Consequential forces: The force which is called into play
when a force is applied on an object is called consequential
force. Frictional force is an example of consequentions force.
(a) State the unit of force and define it.
(b) Name the unit of force in Standard International (SI)
system. How much mass can be lifted by this force in
grams?
(a) Unit of force is kilogram force (kgf). 1 kgf is the force
required to lift a body of mass 1 kg vertically upward.
(b) The unit of force in Standard International (SI) system is
newton (symbol N)
1 newton is the force required to lift the mass of 100 g
vertically upward.
(a) What do you understand by the term force of friction?
(b) Give two examples, where force of friction is a hindrance.
Class-VI Physics
13
Question Bank
Ans.
6.
Ans.
7.
Ans.
8.
Ans.
9.
Ans.
10.
Ans.
(c) State two ways of minimising friction.
(a) A force which acts at the surfaces of contact, when one
body moves upon another body is called force of friction.
(b) Two examples, where force of friction is a hindrances are
(i) it wears out the soles of shoes, and
(ii) it wears out the moving parts of machinery.
(c) Two ways of minimising friction are
(i) by oiling or greasing the moving parts of machinery
(ii) by providing wheels.
(a) When does force of friction come into play?
(b) If a force is applied towards East, in order to move a
body, in which direction does the force of friction act?
(a) The force of friction come into play when one body
moves upon another body.
(b) When a force is applied towards east then the force of
friction will act towards west i.e. opposite to the direction
of force applied.
Why does a knot tied with jute thread not slip easily, as
compared to silk thread?
A knot tied with jute thread not slip easily, as compared to silk
thread because jute thread offers more friction than silk thread.
What would happen if there is no force of friction?
If there is no force of friction, we will not be able to walk, write,
etc..
(a) Define the term pressure.
(b) State and define the SI unit of pressure
(a) Pressure is the thrust (compressive force) acting per unit
area.
(b) The SI unit of pressure is N/m2 i.e. pascal. 1 pascal is the
pressure acting on the surface when a force of 1 N acts
on an area of 1 m2.
Name the types of force that we observe in our daily life.
The types of force that we observe in our daily life are:
(i) Contact force
(ii) Action at a distance force
(iii) Consequential force.
Class-VI Physics
14
14
Question Bank
11. Name the types of force involved in the following:
(i) A rolling ball stops
(ii) A man rowing a boat
(iii) Motion of electric fan
Ans. (i) Frictional force (ii) Muscular force (iii) Electrical force
12. How is the force of friction an advantage?
Ans. The force of friction is very important in our life. Life will not
be possible without friction. Because of friction, we can walk
on the road, we can write on the paper etc. If there is no
frictional force then matchstick could not be lighted by rubbing.
13. How is the force of friction a disadvantage?
Ans. Disadvantages of the force of friction are
(i) it always opposes motion of a body.
(ii) it produces lot of heat and noise at the cost of mechanical
energy. Hence, there is a loss of energy.
(iii) it causes wear and tear of machinery parts which are in
mutual contact.
There are many more disadvantages of friction.
14. Mention three ways in which friction between two surfaces can
be minimised.
Ans. Three ways to reduces the friction between two surfaces are:
(i) by polishing the surfaces (ii) by lubricating, and
(iii) using ball-bearing
15. Mention three ways in which friction between two surfaces can
be increased.
Ans. Three ways to increase the friction between two surfaces are:
(i) by spreading sand and gravel on the slippery ground.
(ii) by providing grooves in the soles of shoes, and
(iii) by providing rough surfaces in the industrial belts to
increase friction.
16. Friction produces heat. Write one advantage and one disadvantage of this property.
Ans. Friction produces heat:
Its one advantage is it converts mechanical energy to heat
energy.
Class-VI Physics
15
Question Bank
Its one disadvantage is it produces lot of heat and noise at the
cost of mechanical energy and hence, there is a loss of energy.
XI. Numerical Problems.
1. You want to lift a heavy box. The force of gravity pulls it
downwards with 500 N.
(a) How much force will you have to apply to lift the box?
(b) If your friend supports the box from below with a force
of 270 N, how much force will you have to apply to lift
the box?
Ans. (a) The minimum force required to lift the box should be equal
to the force of gravity i.e. 500 N.
(b) The required force to apply to lift the box
= 500 N – 270 N = 230 N
2. A horse pulls a cart with a force of 1500 N.
(a) Will the cart move if the force of friction between the cart
and the ground is 2000 N? Why?
(b) Will the cart move if the force of friction between the cart
and the ground is 1000 N? Why?
Ans. (a) No because the frictional force is more than the force
applied by horse to pull the cart.
(b) The cart will move as the force of friction is less than the
force with which horse pulls the cart.
3. Ritu rows a boat with a force of 700 N while running water
applies a force of 500 N. Look at the picture and calculate the
following.
(a) Resultant force while going downstream (that is, the
direction of the river and the boat is the same).
(b) Resultant force while going upstream (that is, the direction
of the river is opposite to the direction in which the boat
is moving).
Class-VI Physics
16
16
Question Bank
Ans. Force with which Ritu rows a boat = 700 N
Force applied by the running water = 500 N.
(a) Resultant force while going downstream
= 700 N + 500 N = 1200 N
(b) Resultant force while going upstream
= 700 N – 500 N = 200 N.
4. A force of 500 N acts on an area of 0.05 m2. Find the pressure
in pascals.
Ans. Force = 500 N
Area = 0.05 m2.
.. .
500 N
500 × 100
Force
Pressure =
=
N/m2
2 =
0
.
05
m
5
Area
= 100 × 100 Pa = 10000 Pa
5. What force will produce a pressure of 50000 Pa on an area of
0.20 m2?
Ans.
Pressure (P) = 50000 Pa
Area (A) = 0.20 m2
Force (F) = ?
P =
F
A
.. .
F = P × A = 50000 × 0.20 N = 10000 N
6. Calculate the area of a body which experiences a pressure of
60000 Pa by a force of 120 N.
Class-VI Physics
17
Question Bank
Ans.
Pressure = 60000 Pa
Force = 120 N
Area = ?
.. .
7.
Ans.
8.
Ans.
9.
Ans.
Area =
=
= 2 × 10–3 m2 = 0.002 m2
Two boys pull a cart in opposite directions. One boy applies
a force of 300 N towards east and other applies a force of
100 N towards west. What is the net force acting on the cart?
As the two boys applying force in opposite direction.
The net force acting on the cart
= 300 N – 100 N
= 200 N towards east
A worker is pulling a cart. The frictional force between the cart
and the ground is 500 N. What is the minimum force that must
be applied by the worker to move the cart?
Since the frictional force between the cart and the ground is
500 N, the minimum force that must be applied is 500 N.
A brick weighing 20 N and having dimensions 25 cm × 10 cm
× 5 cm is kept on the ground in three different ways. Calculate
its pressure in the three cases.
Force = 20 N
Case I:
Pressure, P1 =
=
20 ×100 ×100
25 ×10
= 800 Pa.
Case II:
Class-VI Physics
20 N
10 cm × 5cm
20 ×100 ×100
=
10 × 5
= 4000 Pa
Pressure, P2 =
18
18
Question Bank
20 N
25cm × 5cm
20 × 100 × 100
=
25 × 5
= 1600 Pa.
10. A girl of mass 50 kg is standing on pencil heels each of area
of cross-section 1 cm2 and an elephant of mass 5000 kg and
foot area 250 cm2 each standing on the floor. Which one will
exert more pressure and what is the difference between the
pressure exerted by the girl and the elephant?
Ans. Mass of the girl = 50 kgf = 50 × 10 = 500 N.
Area of the heels = 2 × 1 cm2 = 2 cm2
500 N
.. .
Pressure exerted by girl =
2 cm 2
500 × 100 × 100
=
2
= 2500000 Pa
Mass of the elephant = 5000 kg = 5000 × 10 N
Case III:
Pressure, P3 =
4 × 250
Area of the 4 feet = 4 × 250 cm2 = 100 × 100 m2
.. .
Pressure exerted by elephant =
5000 × 10 × 100 × 100
4 × 250
= 500000 Pa.
Girl will exert more pressure than that of elephant by (2500000
– 500000) Pa = 2000000 Pa.
11. A force F acts on an area of 600 cm2 and produces a pressure
of 12500 Pa. Calculate the magnitude of F.
Ans.
Class-VI Physics
600
Area = 600 cm2 = 100 × 100 m2
19
Question Bank
.. .
Force (F) = ?
Pressure = 12500 Pa
Force = Pressure × Area
= 12500 ×
= 750 N
12. A force of 300 N, while acting on an area A, produces a
pressure of 1500 Pa. Calculate the magnitude of A in cm2.
Ans.
Force = 300 N.
Pressure = 1500 Pa
Area (A) = ?
300 N
1
.. .
Area = Force
1500 P a
5
=
× 10000 cm2
= 2000 cm2.
13. What is the area of cross-section of a body in m2, when it
exerts a force of 50 N and produces a pressure of 2000 Pa?
Ans.
Force = 50 N
Pressure = 2000 Pa
Area = ?
Pressure =
⇒
2000 =
.. .
Area =
m2 =
m2 = 0.025 m2.
****
Class-VI Physics
20
20
Question Bank