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

Two objects of masses 1 kg and 2 kg are moving with velocities 2 m/s and 4 m/s, respectively. They collide and after collision the first object moves at a velocity 3 m/s, then velocity of second object is

A) 3.5 m/s

B) 4.5 m/s

C) 2.5 m/s

D) 0 m/s

Correct Answer: C

Solution :

[c] By the law of conservation of linear momentum,

\[{{m}_{1}}{{u}_{1}}+{{m}_{2}}{{u}_{2}}={{m}_{1}}{{v}_{1}}+{{m}_{2}}{{v}_{2}}\]

\[1\times 2+2\times 4=1\times 3+2{{v}_{2}}\]

\[\Rightarrow \] \[{{v}_{2}}=3.5\operatorname{m}/s\]