Chhattisgarh State Class 9 Science Chapter 5 Solution

Chhattisgarh State Board Class 9 Science Chapter 5 Force and Laws of Motion Exercise Multiple Choice, Fill in the Blanks, Questions and Answers here.

Chhattisgarh State Class 9 Science Chapter 5 Solution

1) Choose the correct option-

(i) The reason for inertia of a body is-

(a) only mass (b) only velocity

(c) mass and velocity both (d) None.

Ans: – option (a) only mass.

(ii) A boy is sitting on the uppermost berth of a train. Just when the train is coming to a halt, hedrops a mango in the open hands of his brother who is sitting on the seat right below him.Where will the mango fall?

(a) right in his brother’s hand

(b) Some distance away from his hand in a direction opposite to the direction of train.

(c) Some distance away from his hands in the direction of the train.

(d)None of this.

Ans: – option (b).

(iii) The concept of rocket launching is based on-

(a) First law of motion (b) Second law of motion

(c) Law of conservation of mass (d) Law of conservation of momentum.

Ans: – The rocket launching is based on Newton third law of motion.

(iv) A ball stops in 0.06 sec. when a force of 500 N is applied to it. The momentum of the ballis-

  • 500 N (b) 500 kgm/s (c) 30 kgm/s (d) 30 N.

Ans: – option (c) 30 kgm/s.

2) Fill in the blanks-

(i) The law of conservation of momentum is applied in the absence of ……….. external forces…………

(ii) Both the ends of a balance are pulled with a weight of 20-20 kg. on each side. The readingon the balance is ……….20…………………

(iii) The first law of motion is also known as the law of ……inertia……………..

(iv) If the acceleration of a body is doubled while keeping its mass constant, the force becomes………….half………….

(v) Force is a ……… vector………………………. quantity.

 

Discuss and Write

1) solids which are made up of aluminium, steel and wood respectively have same shape andvolume. Say which of these solids will have more inertia and why?

Ans: – As moment of inertia is directly proportional to the mass of any object so the moment of inertia will be maximum in steel. The steel has more mass as comparing to the aluminium, wood.

2) Utensils made of glass break on falling on the ground but not when they fall on sand. Why is it so?

Ans: – The kinetic energy is produced while falling on the ground or sand. As this kinetic energy is absorbed by the sand not by the ground so the utensils made up with the glass broken into different parts.

3) Write down the mathematical representation of the second law of motion and write the meaning ofall the symbols used in it.

Ans: – From the second laws of Newton we know that,

F=ma=m (v1 -v2)/t.

Here the F=force; m= mass; t=time taken; (v1 – v2) =change in velocity;

4) Why does a person get a backward push on using a gun.

Ans: – While firing a bullet from gun a push back force is felt. Because of the Newton third law of motion the backwards force is acted. As the force applied to bullet so each an equal force is given by bullet also although its small.

5) Why is the luggage kept on the roof of a bus tied up with a rope?

Ans: – The luggage is tied up with a rope on the roof of a bus as while the bus is in motion there is a chance of it fallen down. The inertia working on the luggage try to remain in position but the bus in motion restricted it.

6) Prove that if the momentum of two bodies is same then the velocity of lighter body will be more thanthe velocity of heavier body.

Ans: –

7) According to the third law of motion, when we apply a force on a body, the body applies equal andopposite force on us. If that body is a car standing aside a road, probably it will not get in motion onthe application of a force by us. A student argues that both the forces here are equal and oppositeand hence they cancel each other. Express your thoughts regarding this argument and tell why thecar does not move in the opposite direction.

Ans: – According to the Newton laws of motion the moment of inertia is the reason behind the state of motion and state of rest of any object. As when we applied force the standing car the car tries to remain in its position so each and equal force are applied to the boy.

8) The velocity of a body of mass 50 kg. moving at a uniform acceleration becomes 7 m/s from 4 m/s in 6 sec. Calculate the initial and final momentum of the body and the force applied on it.

Ans: – As we all know that momentum (p) = mass × velocity.

Here mass is (m) 50kg, v1= 7m/s, v2=4m/s, and time(t) =6sec.

So, p1= 50×7 = 350; and p2=50×4 = 200;

So, the initial and final momentum of the body is 350 and 200.

 

9) A football and a tennis ball are in a similar motion with same velocity. Both of them collide head onwith each other and after some time they come to a stop. If the time interval of collision is 1 sec, then

(i) Which of the two balls will be more affected by the force?

(ii) The momentum of which ball will change more?

(iii) The acceleration of which ball will be greatest?

Ans: – (i) The tennis ball has small mass as compared to the football so it will be affected by the force most.

(ii) The momentum of tennis ball will change more.

(iii) As the mass of the ball of football is maximum and the motion of these two balls is same so the momentum of this ball will be maximum.

10) Prove that the total momentum of two objects remains constant before and after their collision.

Ans: –

11) The force-time graph of a body of mass 3 kg. is drawn in the following figure. Find the momentum of the body during the time interval of 0 to 10 sec.

Ans: –

Updated: January 6, 2022 — 2:22 pm

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  1. I’m very impressed with your answers

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