Question

a truck of mass 20000 kg travelling at 0.5 m/s collides with another truck of half its mass moving in the opposite direction with a velocity of 0.4 m/s. If the trucks couple automatically on collision, calculate the common velocity with which they move.

Answer 1

Both will travel with velocity 0.2 m/sec

Answer 2

M = 20,000 kg
U = 0.5 m/s
m = 10,000 kg
u = - 0.4 m/s (since, it is moving in opposite direction)
let common velocity = v 
therefore common velocity ,
MV+mv = (M+m)u
20,000*0.5 + 10,000*-0.4 = (20,000+10,000)v
10,000-4,000 = 30,000v
6,000 = 30,000v
1/5 = v
0.2 = v
that is common velocity = 0.2m/s
i hope it helps...........