A railway truck of mass `m = 2 xx10^(4)` kg travelling at 0.5 ms^(-1) collides with another of half of its mass moving in the opposite direction with a velocity 0.4 ms. If they collide each other the combined velocity is

Options

A. `0.1ms^(-1)`
B. `0.4ms^(-1)`
C. `0.2ms^(-1)`
D. `0.5ms^(-1)`

Answer

c

Explanation

According to law of conservation of linear momentum,
`m_(1) u_(1)+m_(2) u_(2)=(m_(1)+m_(2))v`
`(2xx10^(4))xx0.5+(1xx10^(4))(-0.4)=(2x10^(4)+1xx10^(4))v`
`[m_(2)=m/2]`
`v=0.2m//s`