Question

A body of mass 10 kg at rest explodes into two pieces of masses 7 kg and 3 kg. If the total Increase in kinetic energy due to explosion is 1680 J, the magnitude of their relative velocity in m/s, after explosion is

• A. $40$
• B. $50$
• C. $70$
• D. $80$

Answer 1

The correct option is A $40$

momentum conservation

$7v=3u$

$KE=1680$

$\frac{7v^2}{2}+\frac{3u^2}{2}=1680$

$v=12m/s$

$u=28$

magnitude of relative velocity is $V=12+28=40$, as they move in opposite direction.