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# Worksheet on Laws of Motion

Q1 A particle is in a straight line motion with uniform velocity. A force is not required :-

a) To increase the speed

b) To decrease the speed

c) To maintain the same speed

d) To change the direction

Q2 Essential characteristic of equilibrium is :-

a) Momentum equals zero

b) Acceleration equals zero

c) K.E. equals zero

d) Velocity equals zero

Q3 When a constant force is applied to a body, it moves with uniform :-

a) Acceleration

b) Velocity

c) Speed

d) Momentum

Q4 A body of mass 40 g is moving with a constant velocity of 2 cm/s on a horizontal frictionless table. The force on the body (in dynes) is :-

a) Zero

b) 39200

c) 160

d) 80

Q5 Working of rocket or jet is based on :-

a) Newton's law

b) Newton's II law

c) Newton's III law

d) All the three laws

Q6 When a horse pulls a wagon, the force that causes the horse to move forward is the force.

a) He exerts on the wagon

b) The wagon exerts on him

c) The ground exerts on him

d) He exerts on the ground

Q7 If the force of gravity suddenly disappears :-

a) The mass of all bodies will become zero

b) The weight of all bodies will become zero

c) Both mas and weight of all bodies will become zero

d) Neither mass nor weight of all bodies will become zero

Q8 A person is standing in an elevator. In which situation he finds his weight less ?

a) when the elevator moves upward with constant acceleration

b) when the elevator moves downward with constant acceleration

c) when the elevator moves upward with uniform velocity

d) when the elevator moves downward with uniform velocity

Q9 The force exerted by a person on the floor of an elevator is more than the weight of the person if the elevator is :-

(a) Going up and slowing down

(b) Going up and speeding up

(c) Going down and slowing down

(d) Going down and speeding up

a) a, c

b) b, c

c) a, d

d) b, d

Q10 The ratio of weights of a man in a stationary lift and in a lift accelerating downwards with a uniform acceleration is 3 : 2. The acceleration of the lift is :-

a) g/3

b) g/2

c) g

d) 4/3 g

Q11 The coefficient of static friction between two surfaces depend on.

a) the nature of surface

b) the shape of the surface in contact

c) the area of contact

d) all of the above

Q12 Assertion :- A player lowers his hands while catching cricket ball.

Reason :- This increases the time of catch.

a) A

b) B

c) C

d) D

Q13 Assertion :- On a rainy day, it is difficult to drive a car or bus at high speed.

Reason :- The value of coefficient of friction is lowered due to wetting of the surface.

a) A

b) B

c) C

d) D

Q14 Assertion :- Angle of repose is equal to the angle of limiting friction.

Reason :- When the body is just on the verge of motion, the force of friction in this stage is called limiting friction.

a) A

b) B

c) C

d) D

Q15 Assertion :- Force of friction depends on the area of contact.

Reason :- Larger the area of contact, larger is the opposition to motion.

a) A

b) B

c) C

d) D

Q16 Assertion :- Static frictional force is a self adjusting force.

Reason :- Force of static friction does not depend upon the mass of the body.

a) A

b) B

c) C

d) D

Q17 Assertion :- The force of tension on a body always acts away from the body.

Reason :- Friction force always opposes the motion of a body.

a) A

b) B

c) C

d) D

Q18 Assertion :- Magnitude of the contact force is always greater than the magnitude of frictional force.

Reason :- Contact force is the resultant of the friction force and normal reaction.

a) A

b) B

c) C

d) D

Q19 Assertion :- Trajectory of a particle depends only on force acting on it.

Reason :- Velocity & position of a particle depends only on force acting on it.

a) A

b) B

c) C

d) D

Q20 Assertion :- If ball is dropped from a higher altitude. There will be a greater value of impulse from ground during collision.

Reason :- Gravity increases momentum of a ball.

a) A

b) B

c) C

d) D

Q21 A man is at rest in the middle of a pond on perfectly smooth ice. He can get himself to the shore by making use of Newton's.

a) first law

b) second law

c) third law

d) law of gravitation

Q22) Why aeroplane fly at low altitudes?

Q23) What is meant by the statement that the body is in equilibrium?

Q24) Why rockets can fly at high altitude?

Q25) Why pulling a lawn roller is easier than pushing?

Q26) Why one should take small steps while walking on ice?

Q27) How can work done by static friction be positive?

1) c

2) b

3) a

4) a

5) c

6) c

7) b

8) b

9) b

10) a

11) a

12) a

13) a

14) b

15) d

16) b

17) c

18) a

19) d

20) a

21) c

22) Aeroplanes always fly at low altitudes because according to Newton’s III law of motion as aeroplane displaces air & at low altitude density of air is high.

23) A body is in equilibrium when net force is zero. A body moving with uniform velocity is also in equilibrium.

24) Rockets move by pushing the exhaust gasses out so they can fly at low & high altitude.

25) Pulling a lawn roller is easier than pushing it because pushing increases the apparent weight and hence friction.

Also pulling is easier than pushing on a rough horizontal surface because normal reaction is less in pulling than in pushing.

26) While walking on ice, one should take small steps to avoid slipping. This is because smaller step increases the normal reaction and that ensure smaller friction.

27) Work done by static friction may be positive because static friction may acts along the direction of motion of an object.

​Work done by static friction on a complete system is always zero but work done by static friction on an object may be +ve, -ve or zero. ​Work done by kinetics friction on a complete system is always –ve.