Question

Two objects collide elastically. The first has a mass of 5.00kg and a

velocity of 8.00 m/s. The second has a mass of 2.50 kg and a velocity
of -4.00m/s. If the velocity of object 1 after the collision is -4.00m/s,
what is the velocity of object 2?

Answer 1

Step-by-step explanation:

General formula

m1 * vi + m2*v2 = m1*v3 + m2*v4

Givens

m1 = 5

m2 = 2.5

v1 = 8 m/s

v2 = - 4 m/s

v3 = -4 m/s

v4 = x

Solution

5 * 8 - 2.5 * 4 = 5 * -4 + 2.5*x

40 - 10 = -20 + 2.5x

30 = - 20 + 2.5x

50 = 2.5x

x = 50/2.5

x = 20 m/s in the positive direction

Remark

Does this answer make sense? It should. You have 5 kg moving 8m/s in the plus direction. That's a lot of momentum. In addition after the collision, it turns around which is more momentum needed.

It has to give up that extra momentum to the 2.5 kg mass.