Quiz 3b (Phys 101 - 11.30am, Spring 2005)
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?
ptot(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.
ptot(after) = (m1+ m2)v = (500 + 500)v = 1000v
Therefore by conservation of total momentum ptot(before) = ptot(after) or 1000 = 1000v.
Hence v = 1m/s.