Page 2 - Class IX-PHYSICS-CH-8- FORCE AND LAWS OF MOTION

b) Is the force balanced or unbalanced on each box ?
c) Which of these represents balanced force?
i) A boy sitting in a chair.
ii) An object sinking in water.
iii) An apple falling from a tree
iv) A magnet attracting a nail
DIRECTIONS for the question 1 to 20: In each of the questions given below, there are
two statements marked as Assertion (A) and Reason (R). Mark your answer as per the
codes provided below:
1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.
5. Both A and R are false.
7.Assertion: If net external force acting on an object is zero, its acceleration is 0.
Reason: Acceleration of an object doesn’t depend on its mass.
8. Assertion: A passenger standing in a moving bus falls forward when the driver
suddenly applies brakes
Reason: The passenger is in a state of unstable equilibrium
rd
9. Assertion: Newton’s 3 law applies to all types of forces. Example, gravitational
electric or magnetic forces, etc.
Reason: Newton’s third law of motion is applicable only when bodies are in motion.
10. Assertion: When a bullet is fired from a gun, there is a forward force on the bullet,
and the recoil of the gun.
Reason: Every action has an equal and opposite reaction.
Subjective Questions:
1. Big cardboard box full of books is lying on the ground. Name the forces which are
acting on it. What kind of force is needed to move the box through a distance (2M)
2. While going to the market, Kashvi’s father asked her to wear a seat belt to avoid
any injury if an accident happened. How can a seat belt help avoid injuries? Do you
think Kashvi’s father is right? If yes, then support his view and justify your answer
by providing a suitable reason. And if no, then give your views on it. (2M)
3. A truck started from rest with the velocity of 45 meters per second in 15 seconds.
The mass of the truck is 3500 kg. Calculate the change in momentum in the force
required. (3M)
4. While playing carrom, the coins are arranged vertically. Anuj observed that a fast
moving striker strikes a pile of carrom coins, and only the bottom coin gets removed and
the vertical arrangement of the coins remains intact.
a) Which law best describes the situation?
b) What is the reason that only the bottom coin is removed, and rest of the coins do not
fall?
c)What is the momentum of a body of mass 2M and velocity V/2. (3M)
CASE BASED QUESTION
1. Shahid and Arun traveled to Mumbai by car.Midway their car broke down. However,
they are able to push the car with uniform velocity on a flat road. The mass of the car
is 1000Kg. To accelerate the car, they take the help of a third person. And when all
the 3 of them push the car an acceleration of 0.5 meter per second square is
produced.