Homework Set #2

PHY 2020
Homework Set #2
Fall 2014
Due: At the start of class on Friday, Sep 5, 2014. (Not 5 minutes after the start of class.)
If you just give an answer without showing how you arrived at that answer, then you will
get no credit for the problem.
1. Bob and Alice are going to race each other. But Alice believes that she is faster than
Bob so she will run 100 m to the finish line, and Bob starts 20 m ahead of Alice. They
begin the race at the same time, and they cross the finish line at exactly the same
time. Alice crossed the finish line after running for 12 s.
(a) How long did it take Bob to cross the finish line?
(b) What was Alice’s speed during the race?
(c) What was Bob’s speed during the race?
2. Now they do something a bit different. Alice and Bob start 100m apart and are now
going to race towards each other. Assume that they are running with the same speeds
as in the first problem.
(a) How far will Alice run before she meets Bob?
(b) How far will Bob run before he meets Alice?
(c) How much time will Bob and Alice be running until they collide?