Question

An empty 20,000 kg coal wagon is moving on a level track at 5 m/s. Suddenly 5000 kg of coal is dumped into it from directly above. The coal initially has zero horizontal velocity. The final speed of the wagon is:

• A. 3 m/s
• B. 2 m/s
• C. 8 m/s
• D. 4 m/s

Answer 1

The correct option is D 4 m/s

According to the problem,

It states that,

Initial momentum=Final momentum

Momentum$=$mass $\times$ velocity

The initial momentum is:

$\left(2000\times 5\right)+\left(5000\times 0\right)$

$=100000Kgm{s}^{-1}$

Final momentum$=(20000+5000)V$

$=25000V$

$25000V=100000$

$=\frac{100000}{25000}$

$V=4m/s$

Hence, the final speed of the wagon is $4m/s$