3) [12 pts] A pendulum is hanging from the ceiling of a train car. a) When the t
ID: 1530930 • Letter: 3
Question
3) [12 pts] A pendulum is hanging from the ceiling of a train car.
a) When the train is stationary, what direction does the pendulum hang?
b) When the train is moving forward at a steady speed along a straight track, what direction does
the pendulum hang?
c) When the train is speeding up as it goes forward, what direction does the pendulum hang?
d) When the train is moving at constant speed around a curved track, what direction does the
pendulum hang?
Explain your reasoning in all cases.
4) [10 pts] The following thought experiment is intended as an exercise in relating different reference frames.
An airplane pilot is flying her open-cockpit Sopwith Camel in a straight horizontal line at a steady speed. She and her copilot are wondering why they are struggling to maintain altitude, when the copilot discovers a bucket of ball bearings left in the back seat by the repair crew. In order to lighten the load, the copilot pours the ball bearings over the side of the aircraft in a more or less steady stream. As viewed by a person standing on the ground, what is the shape of the stream of ball bearings and what direction is it pointing? You may assume that air drag on the bearings is neglegible. Explain your reasoning carefully. (It may help to first consider what the shape of the stream looks like as viewed by the copilot.)
Explanation / Answer
3)(a)When, the train is stationary, the pendulum is in its equilibrium position, the bob is in vertically downward direction.
(b)The pendulum will execute SHM, but starting from backward position with respect to train.
(c)When the train is accelerating, the pendulum swings but begins swinging from backwards direction.
(d)At constant speed, around the curved tracek, the bob will face vertical downward direction.
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