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XI PHYSICS CBSE
Question 1.
A man in a circus jumps from a height of 20 m and is caught by a net spread below him. The
net sags down 3m due to this impact. Calculate the average force exerted by the net on the
man to stop his fall. Take the mass to be 50 kg and consider the value of acceleration during
his free fall AS 10 m/s2.
Question 2
A car starts from rest and accelerates uniformly with 2 m/s2.
At t=15 s, a stone is dropped out of the window (1 m high) of the car. What are the
a.
Velocity and
b.
Acceleration of the stone at t=15.3 s? (Neglect air resistance).
Take g=9.8 m/s2
Question 3
Give the magnitude and direction of the net force acting on a stone of mass 0.2 kg,
(a) just after it is dropped from the window of a stationary train,
(b) just after it is dropped from the window of a train running at a constant velocity of 36
km/h.
(c) just after it is dropped from the window of a train accelerating with
,
(d) lying on the floor of a train which is accelerating with
, the stone being at rest
Relative to the train, neglect air resistance throughout.
Question 4
A 1 kg ball falls from a height of 5m and rebounds to a height of 1. 5 m.Find the change in
linear momentum and average force between the ball and the ground, if the time during
which they are in contact is 0.1s take g = 10 m/s2 .
Question 5
State Newton's Second Law of motion and express it in vector notation.
Question 6
A force of 60 dyne is inclined to the horizontal at an angle of 600. Find the acceleration in a
mass of 6 g, which moves in horizontal direction.
Question 7
Give the magnitude and direction of the net force acting on
(a) a drop of rain falling down with a constant speed,
(b) a cork of mass 10 g at rest
(c) a kite skillfully held stationary in the sky,
(d) a car moving with a constant velocity of 30 km/h on a rough road,
Question 8
A 20 gram bullet moving with 200m/s stops after penetrating a 2 cm of bone. Calculate the
average force exerted by the bullet.
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Question 9
A man is driving a car with a speed of 36 km/hr (roughly 10 m/s). Suddenly a child appears
in the middle of the road. He slams on the brakes, which in turn exerts a retarding force of
1000 N. The mass of the man and the car together is 500 kg. If the child is 27 meters away
from the car when he first hit the brakes, will the child get saved?
Question 10
An object of mass 5 kg is acted upon by two perpendicular forces 8 N and 6 N. Give the
magnitude and direction of the acceleration of the object?
Question 11
Explain why a stone thrown on a glass window smashes the window pane into pieces, but a
bullet from the gun passes through making a clean hole.
Question 12
What do you understand by weight or gravitational force.
Question 13
What do you mean by momentum?
Impulse and Newton's Third Law
Question 1
A hammer of mass 1kg moving with a speed of 6ms-1strikes a wall and comes to rest in 0.1 s.
Calculate
(i) the impulse of force,
(ii) the retardation of the hammer, and
(iii) the retarding force that stops the hammer.
Question 2
If a force exerts an impulse I on the body and changes its speed from u to v, then show that
work done by the force is I (u+v)/2. Given that the force and object's motion is along the
same line.
Question 3
Derive impulse equation.
Question 4
Calculate the recoil velocity V of the gun of mass M when a bullet of mass m is fired with a
horizontal velocity v.
Question 5
What do you understand by impulse?
Question 6
Write any three applications of concept of impulse.
Question 7
Give any four examples of Newton's third law of motion.
Question 8
A spring balance is attached to the ceiling of a lift. A man hangs his bag on the spring and the
spring reads 30N, when the lift is stationary. What will be the reading of the spring balance, if
the lift moves downward with an acceleration of 5 ms-2
Question 9
The terms 'action' and 'reaction' in the third law gives an impression that action comes before
reaction. Is there is any cause-effect relationship?
Question 10
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What is the difference between the working of a jet plane and a rocket?
Question 11
Why chinaware and glassware are wrapped in paper or straw pieces before packing?
Question 12
Why a hammer is used to drive a nail into wood?
Question 13
Why does gun recoil while firing?
Question 14
Newton's third law says that action and reaction are equal and opposite, then how does
motion ever take place?
Common forces in mechanics
Question 1
A mass of 8 kg is suspended by a rope of length 4 m from the ceiling. A force of 40 N in the
horizontal direction is applied at the midpoint P of the rope, as shown. What is the angle the
rope makes with the vertical in equilibrium?
Question 2
The three blocks of mass 4kg, 5kg, and 6kg are suspended with the string, which is passed
over a pulley. Calculate the tension T1, T2, and T3 when the whole system is moving with an
acceleration of 5 m/s2.
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Question 3
A weighing machine inside a stationary lift reads 50kgf, when a man stands on it. What
would happen to the weighing machine reading, if the lift is moving with constant velocity
and constant acceleration?
Question 4
Two forces of 5 kg and 12 kg are connected at the two end of the light inextensible string that
passes over a frictionless pulley. Find the acceleration of the masses and the tension in the
string, when the masses are released.
Question 5
What do you mean by equilibrium of concurrent forces?
Question 6
Consider a book lying on a table. Which forces are acting on the book?
Question 7
A gardener is mowing a lawn by pushing and pulling the machine. In which condition the
normal force is highest?
Question 8
Give the formula of Spring Force and state the significance of the negative sign.
Question 9
What is Normal Reaction? Explain with diagram.
Question 10
What are contact forces? Give some examples of contact and non contact forces.
Circular Motion
Question 1
A circular track of radius 100 m is banked at an angle of 30°. If the coefficient of friction
between the wheels of a car and the road is 0.5, then what is the (i) optimum speed of the car
to avoid wear and tear on its tires, and (ii) maximum permissible speed to avoid slipping?
Question 2
Draw the free body diagram of a car on a banked road and explain which two component of
force provides the necessary centripetal force to move in circular track?
Question 3
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A 1000 kg car rounds a curve on a flat road of radius 50 m at a speed of 14 m/s. Will the car
make the turn or will it skid if the coefficient of friction is 0.60?
Question 4
What is the need of banking a circular road?
Question 5
What do you mean by banking of a curved road and banking angle?
Question 6
Determine the maximum speed with which the vehicle can negotiate curved path safely.
Question 7
Which three forces act on a vehicle during the motion on a level road?
Question 8
Which force provides the necessary centripetal force to the planets to move in circular orbit
around the sun?
Question 9
What is the magnitude and direction of acceleration for a body moving in a circular motion?
Question 10
Explain briefly, how a car is able to go round a level curved path?
Free body problems
Question 1
A 2 kg book is resting on a surface inclined at 30º above the horizontal. Find the normal
force exerted on the book. (take g = 10 m/s2)
Question 2
Free body diagram of three situations are shown below. The net force is known for each
situation. However, the magnitude of few of the forces is not known. Determine the
magnitude of the unknown forces.
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Question 3
Free body diagram of a situation is given below. Determine the net force acting upon the
object.
Question 4.A force is applied on a book resting on a table in rightward direction. Consider the
frictional forces. Draw the free body diagram of the forces acting on the book.
Question 6.Draw free body diagram of two blocks connected with a mass less strings and a
pulley as shown in figure.
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Question 7. Draw free body diagram of two blocks placed one over other as shown in figure.
Question 8
Name the forces which are generally encountered in classical mechanics?
Question 9
What is the need of free body diagram in mechanics?
More on Free body problems
Question 1
Three blocks of different masses are placed one over other on a horizontal surface. Draw the
free body diagram for each block separately.
Question 2
A tractor tows a trailer of mass 1000 kg at a speed of 10 m/s. On level road the tension in the
string is 1000 N. Find the tension in the coupling when the tractor ascends a road having
inclination of 1 in 5.
Question 3
Two blocks A and B of mass 10 kg and 15 kg are connected with a mass less string that runs
on frictionless pulley. Block A moves along a plane that make an angle of 45o with the
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horizontal. The block B moves downward with constant velocity. Find the magnitude of
friction and coefficient of kinetic friction.
Question 5
A block of mass 10 kg rests on a flat wooden floor, the coefficient of friction between block
and floor is 0.5. The block is pulled by a rope making an angle 45o with the horizontal. What
is minimum tension along the rope that just makes the block sliding?
Question 6
A block of mass 5 kg when placed over an inclined plane at an angle of 20o slides down
without acceleration. If the inclination is increased by 10o, then what would be the
acceleration of the block?
Question 7
Two blocks of different masses are pushed along the frictionless surface at an angle. Draw
the free body diagram of both the blocks and of the system. And also mention the forces
acting on them separately.
Question 8.Two wooden blocks A and B are connected to a chord, passing through a
frictionless pulley. Block A is pushed to the left on a surface by a horizontal force. Draw the
free body diagram of both the blocks.
Question 9.A girl pulls a loaded sledge of mass 100 kg along a horizontal surface at constant
velocity in snow. The coefficient of kinetic friction between girl and the snow is 0.10.
Draw its free body diagram and calculate tension in the string. Given = 45o
Question 10.A box of 20 kg is resting on a table. What will be the magnitude of normal force
acting on the box?
Friction
Question 1.Smoothening of surface beyond the limit increases the friction. Why?
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Question 2.A block of mass M is placed on a rough horizontal surface. A force F = mg acts
on the block. If this force is inclined at an angle , considering the coefficient of friction
.Find the relation between and .
Question 3.What happens to the coefficient of friction, when the normal reaction is halved?
Question 4.A ball of mass 1.5 kg lying on floor when given a velocity of 5 m/s is gets
stopped due to friction in 10 s. Calculate the coefficient of friction. Given g = 10 m/s2.
Question 5.Determine the acceleration of the car in which a box lying on its floor will remain
stationary, given that the co-efficient of static friction between the box and the train's floor is
0.25.
Question 6.Ice skating is based on the phenomena of reduced friction. Explain briefly.
Question 7.State the methods to reduce the friction.
Question 8.Explain briefly:
(a) Static Friction
(b) Kinetic friction
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