CID# _________________ Quiz #2 Key
Physics 121 Friday, May 9, 2008
1. Sam and Jon stand on a large, flat, rotating turntable. Sam is 6 feet from the turntable axis; Jon is 12 feet
from the axis. The ratio of the centripetal acceleration experienced by Jon, aJ, to that experienced by Sam
aS, is aJ /aS = (a) 1/4, (b) 1/3, (c) 1, (d) 2, (e) 4.2. An automobile has three accelerating controls, an "accelerator" which produces an acceleration in the
direction of the automobile's motion, a "decelerator" which produces an acceleration anti-parallel to the
automobile's motion, and a "centripetal accelerator" which produces acceleration normal to the
automobile's motion. On a car with a standard transmission a more common name for the centripetal
accelerator is the (a) "accelerator," (b) "brake," (c) "clutch," (d) "gear-shift," (e) "steering wheel."3. A centerfielder catches a fly ball in left centerfield and makes a long throw to the catcher at home plate who
hopes to tag out a base runner who is attempting to score. At what point along the ball's trajectory is its
gravitational acceleration purely centripetal? As it (a) leaves the centerfielder's hand, (b) passes over the
shortstop who is about halfway between the centerfielder and home plate, (c) reaches the catcher's glove.
(d) The gravitational acceleration is everywhere centripetal along the trajectory. (e) The gravitational
acceleration is nowhere centripetal.4. A cruise ship is traveling directly southward with respect to the water in which it is sailing at a speed of 17
knots. The water in which the ship is traveling is part of the Gulf Stream and is flowing northward with
respect to the earth at 2 knots. A woman is walking northward on the ship deck at a speed of 3 knots with
respect to the ship. As she passes her husband who is sitting in a deck chair, she tosses him a jelly bean,
directly eastward with respect to herself, at a speed of 5 knots. The horizontal speed of the jelly bean with
respect to the earth is, in knots, nearest (a) 7, (b) 11, (c) 13, (d) 22, (e) 23, (f) 27.5. A farmer with a pail of milk in his hand realizes that if he swings the pail in a vertical circle with sufficient
speed that the milk will remain in the pail. Furthermore, as a former Ph 121 student, he knows that the
critical speed at which the milk will just remain in the pail is that speed such that the centripetal acceleration
of the whirling pail at the level to which the milk fills the bucket just equals 1 g (and therefore the downward
accelerating milk at the top of the trajectory accelerates no more rapidly than the downward centripetal
acceleration of the pail). If the length of the farmer's arm and bucket, down to the level of the top of the milk,
is exactly 1.0 m, what is the maximum possible period of the rotating milk pail? (a) ½ s, (b) 1 s, (c) 1½ s,
(d) 2 s.