## Laws of Motion Questions and Answers Part-15

1. A ball of mass 150g starts moving with an acceleration of $20 m\diagup s^{2}$ . When hit by a force, which acts on it for 0.1 sec. The impulsive force is
a) 0.5 N-s
b) 0.1 N-s
c) 0.3 N-s
d) 1.2 N-s

Explanation: Impulse = Force * time = m a t
= 0.15 * 20 * 0.1 = 0.3 N-s

2. A body, whose momentum is constant, must have constant
a) Force
b) Velocity
c) Acceleration
d) All of these

Explanation: For a given mass P $\propto$ v . If the momentum is constant then it's velocity must have constant.

3. A rope of length 5m is kept on frictionless surface and a force of 5N is applied to one of its end. Find tension in the rope at 1m from this end
a) 1 N
b) 3 N
c) 4 N
d) 5 N

Explanation:

4. An aircraft is moving with a velocity of $300 m s^{-1}$  . If all the forces acting on it are balanced, then
a) It still moves with the same velocity
b) It will be just floating at the same point in space
c) It will fall down instantaneously
d) It will lose its velocity gradually

Explanation: It still moves with the same velocity

5. A rocket of mass 1000 kg exhausts gases at a rate of 4 kg/sec with a velocity 3000 m/s. The thrust developed on the rocket is
a) 12000 N
b) 120 N
c) 800 N
d) 200 N

Explanation:

6. The momentum is most closely related to
a) Force
b) Impulse
c) Power
d) K.E.

Explanation: Impulse

7. Rocket engines lift a rocket from the earth surface because hot gas with high velocity
a) Push against the earth
b) Push against the air
c) React against the rocket and push it up
d) Heat up the air which lifts the rocket

Explanation: It works on the principle of conservation of momentum

8. A man fires a bullet of mass 200 g at a speed of 5 m/s. The gun is of one kg mass. by what velocity the gun rebounds backwards
a) 0.1 m/s
b) 10 m/s
c) 1 m/s
d) 0.01 m/s

Explanation:

9. A bullet of mass 5 g is shot from a gun of mass 5 kg. The muzzle velocity of the bullet is 500 m/s. The recoil velocity of the gun is
a) 0.5 m/s
b) 0.25 m/s
c) 1 m/s
d) Data is insufficient

a) $0.15\times10^{-3}Ns$
b) $0.98\times10^{-3}Ns$
c) $1.5\times10^{-3}Ns$
d) $2.5\times10^{-3}Ns$