Question

A billiard ball moving with a speed of $5m/s$ collides with an identical ball originally at rest. If the first ball stops after collision, then the second ball will move forward with a speed of

• A. $10m{s}^{-1}$
• B. $5m{s}^{-1}$
• C. $2.5m{s}^{-1}$
• D. $1.0m{s}^{-1}$

Answer 1

The correct option is B $5m{s}^{-1}$

Since There is no external force, we can apply momentum conservation,

$P_1=m\left(V\right)=5m$

$P_2=0$

$P_i=5m+0=5m$

and $P_f=m\times 0+m{v}_2$

$P_i=P_f$

$5m=m{v}_2$

$v_2=5m/s$

we can also conclude that Due to elastic collision of bodies having equal mass, their velocities get interchanged.