Question

A railway wagon of mass ${10}^{5}kg$ is moving with a velocity of $0.5m{s}^{-}1$ beneath a stationary coal dumper. When $2\times {10}^{5}kg$ of coal is dropped into it, the velocity of the wagon would be

• A. $0.333m{s}^{-1}$
• B. $0.167m{s}^{-1}$
• C. $0.233m{s}^{-1}$
• D. $0.133m{s}^{-1}$

Answer 1

The correct option is B $0.167m{s}^{-1}$

Using conservation of linear momentum : $P_i=P_f$

So, $MV=M_2{V}_2$

Or ${10}^5\times 0.5=(1+2)\times {10}^5{V}_2$

$⟹V_2=0.167m/s$