PHY 2020
Homework Set #9
Fall 2014
Name:
Due: At the start of class on Friday, Oct 24. 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.
For these problems, you must include the appropriate units with your answers.
1. The lower-case Greek letter ω is often used to describe the rate of rotation of some
object, that is the angular velocity of the object, for example the minute-hand of a
watch. The units of ω are radians/second, and 2π radians = 360◦ , and ω = v/R,
where R is the radius.
(a) What is the the angular velocity ω of the second hand of a watch in units of
radians per second?
(b) If your watch (assuming it is an old fashioned watch) runs too slowly and loses
one half-minute every minute, then what is ω for your not-very-accurate watch?
(c) What is the approximate value of the angular velocity ω of the Earth as it rotates
around the sun, in units of radians per second?
2. The second hand on your watch is 1 cm long.
(a) What is the speed of the tip of the second hand as it rotates around your watch?
Make sure that the units of your answer are cm/s.
(b) What is the magnitude of the acceleration of the tip of the second hand of your
watch? Make sure that the units of your answer are cm/s2 .