Question

Two cars of equal mass collide on a horizontal frictionless surface. Before the collision, car a is at rest while car b has a constant velocity of 12 m/s. After the collision the two bodies are stuck together. What is the speed of the composite body (a + b) after the collision?

Answer 1

Let v be the required speed of the composite body.

CAR a

mass = m

velocity = v' = 0 m/s

CAR b

mass = m

velocity = v'' = 12 m/ s

since it is inelastic collision

the total momentum is conserved

m v' + m v'' = (m+m)v

m(0)  + m (12) = 2 m v

12 m  = 2 m v

v = 6 m/s

THE REQUIRED VELOCITY IS 6 m/s