Question

A railway carriage of mass 10 tonne moving with a velocity of 12 m/s catches up with another carriage of mass 20 tonne moving with a velocity of 6 m/s and is coupled with it. Moving together, the two carriages collide and couple with a third carriage of mass 7.5 tonne, which is at rest. Find the velocity with which the three carriages move.

Answer 1

Momentum before collision and after all collision is conserved.

$\Rightarrow 10\times 12+20\times 6+7.5\times 0=\left(37.5\right)v$

$\Rightarrow v=\frac{120+120}{37.5}=\frac{240}{37.5}$

Combined velocity $v=6.4m/s.$

Hence, the answer is $6.4m/s.$