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III.! [30 points total] The diagram at right represents a strobe photograph of a skydiver
who jumps off a hovering helicopter at instant t1. At instant t6, the skydiver reaches
“terminal velocity” (i.e., starts to move with constant speed due to air resistance).
Recall that for a strobe diagram, the positions are shown at instants separated by equal
time intervals.
A.! [5 pts] Is the magnitude of the average velocity of the skydiver between instants
2 and 5 greater than, less than, or equal to the magnitude of the average velocity
of the skydiver between instants 6 and 9? Explain how you could use the strobe
diagram to determine your answer.
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B.! [4 pts] Draw a vector indicating the direction of the change in velocity between
instants 2 and 5. If the change in velocity is zero, state so explicitly. Explain how
you used the strobe diagram to determine your answer.
Direction of Δv
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C.! [5 pts] Is the magnitude of the average acceleration of the skydiver between
instants 2 and 5 greater than, less than, or equal to the magnitude of the average
acceleration of the skydiver between instants 6 and 9? Explain.
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D.! [6 pts] Is the magnitude of the average net force acting on the skydiver between instants 2 and 5
greater than, less than, or equal to the magnitude of the average net force acting on the skydiver
between instants 6 and 9? Explain.
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E.! [10 pts] Consider the forces acting on the skydiver at two consecutive instants, 5 and 6.
i.! Is the magnitude of the gravitational force on the skydiver at instant 5 greater than, less
than, or equal to that at instant 6?
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ii.! What can you conclude about the magnitude and direction of the air resistance at instant
6?
iii.! Is the magnitude of the air resistance on the skydiver at instant 5 greater than, less than,
or equal to that at instant 6?
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Physics!114A,!Autumn!2016!
Exam!1!
Page!6!