two test cars of equal mass moving towards each other collide on a horiontal frictionless surface. Before the collision, car A has a constant speed 20m/s while car B has a constant speed of 12m/s. After the collision, the two bodies are stuck together. What is the speed of the composite body (A+B) after the collision?

4 m/s

Explanation:

m1 = m2 = m

u1 = 20 m/s, u2 = - 12 m/s

Let the speed of composite body is v after the collision.

Use the conservation of momentum

Momentum before collision = momentum after collision

m1 x u1 + m2 x u2 = (m1 + m2) x v

m x 20 - m x 12 = (m + m) x v

20 - 12 = 2 v

8 = 2 v

v = 4 m/s

Thus, the speed of teh composite body is 4 m/s.