Question

a railway truck of mass 10000 kg travelling at 1 m per sec collides with another of double its mass moving in a opposite direction with velocity 0.2 ms-1. If the truck couples automatically on collision their common velocity is in ms-1

Answer 1

Hy

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 

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