11/10/2014 HW_Week2
http://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=2992507 1/29
HW_Week2
Due: 11:59pm on Friday, September 12, 2014
You will receive no credit for items you complete after the assignment is due. Grading Policy
Speed of a Bullet
A bullet is shot through two cardboard disks attached a distance apart to a shaft turning with a rotational period , as
shown.
Part A
Derive a formula for the bullet speed in terms of , , and a measured angle between the position of the hole in
the first disk and that of the hole in the second. If required, use , not its numeric equivalent. Both of the holes lie at
the same radial distance from the shaft. measures the angular displacement between the two holes; for instance,
means that the holes are in a line and means that when one hole is up, the other is down. Assume that
the bullet must travel through the set of disks within a single revolution.
Hint 1. Consider hole positions
The relative position of the holes can be used to find the bullet's speed. Remember, the shaft will have
rotated while the bullet travels between the disks.
Hint 2. How long does it take for the disks to rotate by an angle ?
The disks rotate by 2 in time . How long will it take them to rotate by ?
Give your answer in terms of , , and constants such as .
Hint 1. Checking your formula
If your formula is correct, when you plug 2 in for , your answer will be .
ANSWER:
2 J
R
J
J - J - R