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?
Question
Answer:
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.