# Important questions for Class 9 science force and laws of motion

Important questions for Class 9 science force and laws of motion

1. The people in the bus are pushed backwards when the bus starts suddenly due to:- (a) Inertia due to Rest (b) Inertia due to Motion (c) Inertia due to direction (d) Inertia.
2. If the force acting on the body is zero. Its momentum is :-  (a) zero (b) constant (c) Both (d) None
3. The inability of the body to change its state of rest or motion is :-                 (a) Momentum  (b) Force (c) Inertia (d) Acceleration.
4. Which law explains swimming?  (a) Newton’s first law  (b) Newton’s second law  (c) Newton’s third law (d) All of these
5. Why does the passenger sitting in a moving bus are pushed in the forward direction when the bus stops suddenly?
6. Why does the boat moves backwards when the sailor jumps in the forward direction?
7. Derive the law of conservation of momentum from Newton’s third law?
8. An astronaut has 80 Kg mass on earth. What is his weight on earth? what will be his mass are weight on mars where g = 3.7 m/s2
9. A boy throws a stone up with a velocity of 60 m/s. How long will it take to reach the maximum height (g = -10m/s2) What will be the maximum height reached by the stone? What will be its velocity when it reaches the ground?
10. A certain particle has a weight of 30N at a place where the acceleration due to gravity is 9.8m/s2 What are its mass and weight at a place where acceleration due to gravity is3.5m/s2
11. What will be its mass & weight at a place where acceleration due to gravity is zero? Why does a person while firing a bullet holds the gun tightly to his shoulders?
12. A car is moving with a velocity of 16m/s when brakes are applied. The force applied by the brakes is 1000N. The mass of the car its passengers is 1200Kg.
13. How long should the brakes be applied to make the car come to a halt?
14. How for does the car travel before it comes to rest?
15. A body of mass 2Kg is at rest at the origin of a frame of reference. A force of 5 N acts on it at t = 0. The force acts for 4S and then stops. What is the acceleration produced by the force on the body. What is the velocity at t= 4s
16. Newton’s first law of motion is also called:-(a) Law of Inertia (b) Law of Momentum (c) Law of Action & Reaction (d) None of these
17. If the friction acting on the body is more the body will move:-(a) More speedily (b) Less speedily  (c) Same speed (d) None of these
18. The S.I. unit of weight is :- (a) Newton (b) Newton m (c) Newton/sec  (d) Newton m/s
19. State Newton’s first law of Motion?
20. A body of mass 5Kg starts and rolls down 32m of an inclined plane in 4s. Find the force acting on the body?