A 2.0-kg mass moving at 5.0 m/s suddenly collides head-on with a 3.0-kg mass at rest.If the collision is perfectly inelastic,what is the speed of the masses just after the collision?
A)10 m/s
B)2.5 m/s
C)2.0 m/s
D)0 m/s,since the collision is inelastic

Question

Quizplus · Accepted Answer

In a perfectly inelastic collision, the two objects stick together and move with a common velocity after the collision. Using conservation of momentum:

initial momentum = final momentum 
m1v1 + m2v2 = (m1 + m2)v

where m1 is the mass of the 2kg object, v1 is its initial velocity (5m/s), m2 is the mass of the 3kg object, v2 is its initial velocity (0m/s), and v is the final velocity of the combined objects.

Plugging in the numbers: 
(2kg)(5m/s) + (3kg)(0m/s) = (2kg + 3kg)(v) 
10kg m/s = 5kg v

Therefore, v = 2 m/s.

A 20-Kg Mass Moving at 5