Question

A car of mass 400 kg travelling at 72 kmph crashes a truck of mass 4000 kg and travelling at 9 kmph in the same direction. The car bounces back with a speed of 18 kmph. The speed of the truck after the impact is

• A. 9 kmph
• B. 18 kmph
• C. 27 kmph
• D. 36 kmph

Answer 1

The correct option is B 18 kmph

Using momentum conservation,

$m_{car}{u}_{car}+m_{truck}{u}_{truck}=m_{car}{v}_{car}+m_{truck}{v}_{truck}$

$400\times 72+4000\times 9=-18\times 400+4000\times v$

$v=18kmph$