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

Name: _________________Answers_____________________

1. What does to conserve mean in Physics?

To keep constant

2. A railway car weighing 500kg is traveling at 2m/s along a railway track. It collides with a stationary railway car of weight 500kg. 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 = 500x2 + 500x0 = 1000 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 = (500 + 500)v = 1000v

Therefore by conservation of total momentum p_tot(before) = p_tot(after) or 1000 = 1000v.

Hence v = 1m/s.