PHY 2020
Homework Set #8
Fall 2014
Name:
Due: At the start of class on Wednesday, Oct 22, 2014. (Not 5 minutes after the start of
class.)
Homework set #9 will be posted on Wednesday, Oct 22, and will be due on Friday, Oct
25.
If you just give an answer without showing how you arrived at that answer, then you will
get no credit for the problem.
For these problems, you must include the appropriate units with your answers.
1. A block M2 of mass 2 kg is moving on a frictionless surface with a speed of 3 m/s until
it bumps into a block M1 of mass 1 kg. The two blocks then stick together and keep
on moving with a constant speed.
(a) How much kinetic energy did M2 have before the collision occurred?
(b) How much kinetic energy did M1 have before the collision occurred?
(c) What is the speed of the two blocks after they stick together?
(d) How much kinetic energy do the combined blocks have after the collision?
2. A powerful spring is held compressed between a block M1 of mass 1 kg and another
block M4 of mass 4 kg. The two blocks are then released simultaneously, they move
off on a frictionless surface in opposite directions, and M4 is measured to have a speed
of 2 m/s. What, then, is the speed of M1 ?