Quiz 3a (Phys 101 - 11.30am, Spring 2005)

Name: ________________Answers______________________

1. What does to conserve mean in Physics?

To keep constant

2. A railway car weighing 1000kg is traveling at 2m/s along a railway track. It collides with a stationary railway car of weight 1000kg. After the collision the two cars stick together and travel at a speed v.

a) Determine the total momentum of the two cars before the collision?

p_tot(before) = m₁v₁ + m₂v₂ = 1000x2 + 1000x0 = 2000 kg m/s

b) Use the Law of Conservation of Momentum to determine the speed v after the collision.

p_tot(after) = (m₁+ m₂)v = (1000 + 1000)v = 2000v

Therefore by conservation of total momentum p_tot(before) = p_tot(after) or 2000 = 2000v.

Hence v = 1m/s.