Question

A truck moving on horizontal road towards east with velocity $20m{s}^{-1}$ collides elastically with a light ball moving with velocity $25m{s}^{-1}$ along west. The velocity of the ball just after collision :

• A. $65m{s}^{-1}$ toward east
• B. $25m{s}^{-1}$ towards west
• C. $65m{s}^{-1}$ towards west
• D. $20m{s}^{-1}$ towards east

Answer 1

The correct option is A $65m{s}^{-1}$ toward east

Taking east as positive direction.
velocity of approach$=25-(-20)=45m/s$
velocity of separation$=v-20$
elastic collision, e$=1$ ,velocity of approach$=$velocity of separation
$v-20=45v=65m/s$