Q. Two perfectly elastic objects $A$ and $B$ of identical mass are moving with velocities 15 $ms^{- 1}$ and 10 $ms^{- 1}$ respectively, collide along the direction of line joining them. Their velocities after collision are respectively
A) 10 $ms^{- 1}$ ,15$\ ms^{- 1}$
B) 20$\ ms^{- 1},5\ ms^{- 1}$
C) 0$\ ms^{- 1},25ms^{- 1}$
D) 5$\ ms^{- 1},20ms^{- 1}$
Explanation
(a) $15m + 10m = mv_{1} + mv_{2}$
$25 = v_{1} + v_{2}$
And $\frac{v_{2} - v_{1}}{u_{1} - u_{2}} = 1$
$\Rightarrow \ \ \frac{v_{2} - v_{1}}{15 - 10} = 1$
$\Rightarrow \ \ \ v_{2} - v_{1} = 5$
Solving Eqs. (i) and (ii), we have
$v_{2} = 15ms^{- 1},v_{1} = 10ms^{- 1}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.