A 2000-kg truck is sitting at rest (in neutral) when it is rear-ended by a 1000-

Question

A 2000-kg truck is sitting at rest (in neutral) when it is rear-ended by a 1000-kg car going 20m/s .After the collision, the two vehicles stick together.

1)What is the final speed of the car-truck combination?

2)What is the kinetic energy of the two-vehicle system before the collision?

3)What is the kinetic energy of the system after the collision?

4) Based on the results of the previous parts, what can you conclude about which type of collision this is? Elastic, Inelastic, or totally inelastic?

5) Calculate the coefficient of restitution for this collision.

Explanation / Answer

mass m1= 2000 kg
intial velocity u1 = 0
mass m2 = 1000 kg
u2 = 20 m/s
1)
from conservation of momentum
m1u1+m2u2 =(m1+m2)V
V = 6.67 m/sc
2)
kinetic emenrgy befor collision = 0.5mu1^2 + 0.5 m2u2^2

0 + 0.5*1000*20^2 = 200000 J
3)
kinetic energy after
0.5(m1+m2)V^2 = 0.5(1000+2000)6.67^2 = 66673 J
4)
totally inelastic
5)
coefficient of restitution = relative speeds after collision / relative speeds before collision

= 6.67/20-0 = 0.335

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