Superior Lalazar Public School and College Thana
www.slpsorg.com 0932-442385 email. 0917351@rgu.ac.uk
Solved Physics 9th 2013 paper Malakand Board.
Section B (Marks 32)
Q. 2 Answer any eight parts. Each part carries 4 marks
(i) Why steam at 100C produces more severe burns than boiling
water at 100C
The steam at 100C produces more severe burns than boiling water at
100C because steam have latent heat of vaporization which is much
higher than latent heat of boiling water. The severe burn is due to high
amount of heat steam passes to the human body.
(ii) What is Pascal principle? Write its practical application.
Pascal Principle
“ All liquids transmit pressure equally in all direction”
In other words
"When pressure on any portion of a confined liquid is changed, the
pressure on every other part of the liquid is also changed by the same
amount."
Pascal's Law has a number of applications in our daily such as:
i)
• Hydraulic Brakes
ii) • Hydraulic Press
iii) • Hydraulic Lift
(iii) Is the distance covered by a body may be greater than the
magnitude of the dispalacement?
Ans. Yes, it is possible because distance is the total length of the
actual path followed by a body during its motion, but displacement is
the shortest distance between initial and final position in a particular
direction. For example, when a body does not move in a straight line
but moves in a curved path then distance will be greater than
displacement.
(iv) How we can find the volume of a small pebble with the help of
measuring cylinder?
a. Take water in a measuring cylinder
b. Note the initial volume of water by V1
c. Drop the pebble in the cylinder gently
d. Note the final volume after dropping pebble inside by V2
e. Now subtract V1 from V2
f. The difference will be the volume of pebble or irregular shape
body
(v) Explain why white cloths are preferred wearing in summer?
Ans
The white cloths are preferred wearing in summer because white colour
is bad absorbent but good reflector of sun light so keep our body cool
due to which we feel comfortable in summer.
(vi) Moon is attracted by earth why it does not fall on earth?
Moon is attracted by the earth but it does not fall on earth because the
gravitational force of attraction between moon and earth provides
centripetal force which keeps the moon in motion around the earth and
tangential velocity of moon is very high which prevents moon from
falling.
(vii) Why a bootman tie his boat to a pillar before allowing the
passengers to step on the river bank?
When passengers jump from the boat they apply some force on
the boat with their feet in backward direction which produce
backward motion in boat. Therefore the boat is tied with pillar
to keep the boat in static position so that passengers move out
from the boat easily.
(viii) Distinguish between base and derived quantities. Give two
examples of each
Ans See solved paper Mardan board answer in Section B Q 2 (i)
(ix) Why a small needle sinks in water and huge ships travel easily
in water with out sinking?
The small needle sinks in water because weight of the needle is greater
than the weight of water displaced by needles so upthrust is less than
downward weight. In contrast the huge ships easily travel in water
without sinking because the weight of ships is less than the weight of
water displaced by ships so upthrust is greater than downward weight
of ships.
(x) Define work and its unit joule. Give mathematical expression of
work
Ans. See solved paper Mardan board answer in Section B Q 2 (vi)
(xi) how much heat is required to increase the temperature of 0.5Kg
of water from 10C to 65C (C= 4200J/KgK)
Ans. See example 8.6 page 174
Given Data;
Mass of water m = 0.5Kg
Initial temperature T1 = 10C
Final temperature T2 = 65 C
Specific heat of water C = 4200J/KgK
Required Data:
Heat required ∆Q = ?
Solution:
Rise in temperature ∆T = T2-T1 = 65-10 = 55C
∆Q = cm∆T = 4200 x 0.5 x 55 = 115500J
Section C
Q. 3 (i) Derive Vf= Vi + at by graphical method
Consider a body which has initial velocity ‘Vi’ and this body
accelerates uniformly, then after time ‘t’ its final velocity will
become Vf at uniform acceleration. Now consider velocity time
graph shown in figure 1
AD = DC/AC---------- (1)
but AD= a (slope of graph is acceleration), DC= ΔV and AC= t
putting the values in equation -1
a = ΔV/t or at = ΔV (2)
but ΔV= Vf-Vi
therefore at= Vf-Vi or Vf= Vi + at
Vf= Vi + at (first equation of motion)
Q 3 (ii) A truck moving at a speed of 20m/s begins to slow at
constant rate of 3m/S2 find how far it goes before stopping.
Ans See videos lecture chap 2 Q 3
Q 4 (i) What is mean by force? State second law of motion and give
its mathematical expression.
FORCE
"Force is an agent which changes or tends to change the state of rest or
of uniform motion of a body."
Force is a vector quantity and SI unit is Newton
SECOND LAW OF MOTIONS
STATEMENT
"When a force acts on an object it produces an acceleration which is
directly proportion to the amount of the force and inversely
proportional to the product of mass"
EXPLANATION
According to the Newton`s Second law of motion when a force acts
on an object it produces an acceleration which is directly proportion
to the amount of the force and inversely proportional to the product
of mass
Combining equation i and ii
where k is constant of proportionality
If the Value of K is 1
so,
a = F/m
or
F = ma
SECOND STATEMENT
With the help of above equation 2nd law of motion can be expressed as:
The net force acting on a body is equal to the product of the mass of
body and the acceleration produced in it.
Q 4 (ii) a 5Kg object is placed on a horizontal wooden surface how
much force is required to set in it motion. (u = 0.6 g= 10m/s2)
Ans. Given data
Mass of the object m= 5Kg
= 0.6 g= 10m/s2
Required data : Force F = ?
Formula used: F = Fn =
W=
mg
Solution; F = mg = 0.6 x 5 x 10 = 30N
So minimum force required will be 30N
Q 5 (i) Find mass of earth with the help of universal gravitation law
where G (6.67 x 10-11 Nm2/kg2) and Re (6.4x106m).
MASS OF EARTH:
Consider a body of mass m which is lying on the surface of earth. Let
the mass of earth is Me and radius is Re.
The gravitational force between earth and body mass m will be
𝐺𝑀𝑒𝑚
F=
------(1)
𝑅𝑒2
But the force with which the earth attracts a body towards its centre is
called weight so
F= W= mg
Putting the value of F in above equation 1
mg =
𝐺𝑀𝑒𝑚
𝑅𝑒2
𝐺𝑀𝑒
g=
𝑅𝑒2
OR
Me=
𝑔𝑅𝑒2
𝐺
---(2)
By putting the value of g(10m/sec2 MASS OF EARTH:
The mass of earth was determined by Newton with the help of law of
gravitation. Consider a body of mass m which is lying on the surface
of earth. Let the mass of earth is Me and radius is Re.
The gravitational force between earth and body mass m will be
𝐺𝑀𝑒𝑚
F=
------(1)
𝑅𝑒2
But the force with which the earth attracts a body towards its centre is
called weight so
F= W= mg
Putting the value of F in above equation 1
mg =
𝐺𝑀𝑒𝑚
𝑅𝑒2
𝐺𝑀𝑒
g=
𝑅𝑒2
OR
𝑔𝑅𝑒2
Me=
---(2)
𝐺
By putting the value of g(10m/sec2), G (6.67 x 10-11 Nm2/kg2) and
Re (6.4x106m) we will get the value of Me
Me=
9.8 𝑥(6.4x106m)2
6.67 x 10−11
Me = 6x 1024Kg
) we will get the value of Me
Me=
9.8 𝑥(6.4x106m)2
6.67 x 10−11
Me = 6x 1024Kg
Q 5 (ii) how much energy is generated when 1gram of mass is
completely converted into energy?
Ans. Given data
Mass m= 1g = 10-3Kg
Velocity of light c= 3x108 m/s
Required data.
Energy = ?
Formula used.
E= mc2
Solution. E= mc2 = 10-3Kg x 3x108 m/s =
9x1013J
Q. 6 (i) Explain rectangular components of a vector
with the help of examples.
Ans. The two components of a vector which make right angle (900)
with each other is called rectangular components of that vector.
Consider vector F which makes angle ᶿ with x-axix. Draw
perpendicular from head of F on x-axis. So OB and AB are
rectangular components of vector F which can also be represented by
Fx and Fy. The Fx is called horizontal component while Fy is called
vertical component of vector F
Q 6 (ii) a force of 100N is applied perpendicularly at a distance of
0.50m to turn a nut of the wheel of a bus. Find the torque acting on the
nut.
Ans see video lectures Q 1 chapter No 4
Superior Lalazar Public School and College Thana
www.slpsorg.com 0932-442385 email. 0917351@rgu.ac.uk
Solved Physics 9th 2013 paper Malakand Board.