# CBSE Class 9 Science Important Question Chapter 9 Force and Laws of Motion

## Part-1

Q.1. State Newton’s first law of motion.

Q.2. An athelete always runs some distance before taking a jump. Why?

Q.3. Define 1 kg weight and express it in newton.

Q.4. What is the mass of an object whose weight is 196 N?

Q.5. Two similar vehicles are moving with the same velocity on the roads such that one of them is loaded and the other one is empty. Which of the two vehicles will require larger force to stop it ? Give reasons.

Q.6. Is it possible that the train in which you are sitting appears to move while it is at rest?

Q.7. Why do passengers in a bus tend to fall backward when it starts suddenly.

Q.8. Which one has greater inertia : a stone of mass 1 kg or a stone of mass 5 kg ?

Q.9. Name the physical quantity which is determined by the rate of change of linear momentum.

## Part-2

Q.10. Define the term ‘force’.

Q.11. Name two effects a force can bring about, other than moving or stopping a body.

Q.12. What do you understand by the term inertia?

Q.13. What determines the magnitude of inertia of a body?

Q.14. Which has more inertia, a table tennis ball or a rubber ball of the same size?

Q.15. What do you understand by the term momentum?

Q.16. State two factors which determine the momentum of a body.

Q.17. Is momentum a scalar or a vector quantity?

Q.18. State the SI unit of momentum.

Q.19. A body P has mass 2 m and velocity 5 v. Another body Q has mass 8 m and velocity 1.25 v. Which of the two has more momentum?

Q.20. The magnitude of a physical quantity is 8.5 N-s. Name the physical quantity.

Q.21. State the law of conservation of momentum.

Q.22. State Newton’s third law of motion.

Q.23. State two factors which determine the force possessed a body.

Q.24. Name and define the unit of force in SI system.

Q.25. A force of 36 N acts on a body of mass 12 kg. What is the acceleration of the body?

Q.26. A body is acted by a force of 15 kg f. What is force acting on a body in SI system?
Take ‘g’ = 9.8 m/s2

Q.27. What is the mass of a body having a force of 5.7 kg f?

## II. Short Answer Questions (2 marks)

Q.28. What would happen if a fielder stops the fast moving ball suddenly? Justify your answer.

Q.29. (a) Why does the rider fall in the forward direction when a running horse stops suddenly?
(b) Why is it easier to stop a tennis ball in comparison to a cricket ball moving with the same speed ?

Q.30. A bullet of mass 25 g is fired horizontally with a velocity of 100 m/s from a gun of mass 5 kg. Calculate the recoil velocity of the gun.

Q.31. Why do we jerk wet clothes before spreading them on line?

Q.32. Give reasons for :
(a) When a carpet is beaten with a stick, dirt comes out of it.
(b) It is difficult for a fireman to hold a hose which ejects large amount of water at high velocity.

Q.33. (a) State Newton’s third law of motion.

(b) In collision between a heavier body and a lighter body, how do the forces experienced
by the two bodies compare ?

Q.34. Which is having higher value of momentum ? A bullet of mass 10 g moving with a velocity of 400 m/s or a cricket ball of mass 400 g thrown with the speed of 90 km/hr.

Q.35. A hammer of mass 500 g, moving at 50 ms–1, strikes a nail. The nail stops the hammer in a very short time of 0.01 s. What is the force of the nail on the hammer ?

Q.36. Calculate the force required to produce an acceleration of 2 ms–2 in a body of mass 10 kg.

Q.37. It is difficult to balance our body when we accidentally slip on a peel of banana. Explain why?

Q.38. A bullet of mass 50 g is horizontally fired with a velocity of 35 m/s form a pistol of mass 4 kg. Calculate the recoil velocity of the pistol.

Q.39. It is dangerous to jump out of a moving bus. Explain why ?

Q.40. While catching a fast moving ball, fielder gradually pulls his hand backwards. Give
reasons.

Q.41. Give a simple experiment to illustrate the inertia of rest.

Q.42. In the above experimental set-up, a student given the card a sharp, fast horizontal flick with a finger.
(a) What will happen to the coin?

Q.43. In the figure above, a pile of similar coins is hit very strongly at the bottom of the pile by a striker. What will happen to the :
(i) Lowest coin (ii) Rest of the coins (iii) Why ?

## Other Important Questions

Q.44. Why do fruits fall down from the branches of tree, when the branches are shaken vigorously? Explain.

Q.45. Why is it dangerous to jump out of a moving vehicle? How can the danger be minimised?

Q.46. Why are we not hurt at all, while diving in a deep water tank from a height of 10 m?

Q.47. Why are long jump athletes made to jump in sand pits?

Q.48. Why are glass or porcelain articles packed in straw or foam?