Worksheet: Force and Laws of Motion - Science Class 9

Q.1. Fill in the blanks
(i) When a running car stops suddenly, the passengers are jerked ___________.
(ii) In collisions and explosions, the total _________ remains constant, provided that no external ___________ acts.
(iii) If there were no unbalanced force of ___________ and no _________ resistance, a moving bicycle would go on moving for ever.
(iv) When a stationary car starts suddenly, the passengers are jerked ___________.
(v) To every action, there is an ___________ and __________ reaction.

Q.2. The inability of the body to change its state of rest or motion is :-
(a) Momentum
(b) Force
(c) Inertia
(d) Acceleration.

Q.3. The S.I. unit of weight is:
(a) Newton
(b) Newton m
(c) Newton/sec
(d) Newton m/s

Q.4. A batsman hits a cricket ball which then rolls on a level ground. After covering a short distance, the ball comes to rest. The ball slows to a stop because
(a) the batsman did not hit the ball hard enough.
(b) velocity is proportional to the force exerted on the ball.
(c) there is a force on the ball opposing the motion.
(d) there is no unbalanced force on the ball, so the ball would want to come to rest.

Q.5. If the initial velocity is zero then the force acting is :-
(a) Retarding
(b) Acceleration
(c) Both
(d) None.

Q.6. An object experiences a net zero external unbalanced force. Is it possible for the object to be travelling with a non-zero velocity? If yes, state the conditions that must be placed on the magnitude and direction of the velocity. If no, provide a reason.

Q.7. Why do you fall in the forward direction when a moving bus brakes to a stop and fall backwards when it accelerates from rest?

Q.8. Why is the weight of the object more at the poles than at the equator?

Q.9. Explain why some of the leaves may get detached from a tree if we vigorously shake its branch.

Q.10. Why is it advised to tie any luggage kept on the roof of a bus with a rope?

Q.11. Why does the passenger sitting in a moving bus are pushed in the forward direction when the bus stops suddenly?

Q.12. State Newton’s first law of Motion?

Q.13. Define force and what are the various types of forces?

Q.14. State Newton’s second law of motion?

Q.15. When a carpet is beaten with a stick, dust comes out of it. Explain.