9th Class Science Force and laws of motion Question Bank MCQs - Force and Laws of Motion

A bullet of mass 30 g is fired horizontally with a velocity of 120 m/s from a pistol of mass 2 kg, the recoil velocity of the pistol is

A) 1.6 m/s

B) 2.8 m/s

C) 2.4 m/s

D) 1.8 m/s

Correct Answer: D

Solution :

[d] By the law of conservation of momentum,

Initial momentum = Final momentum

0 = 0.03 \[\times \] 120 +2\[\times \] v

where, v is recoil velocity.

0=3.6+2v

\[v=\frac{-3.6}{2}=1.8m/s\]

Here, negative sign is for recoiling in opposite directions.