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Quiz #6 Key
Biomechanics
IPHY 4540
0.5 points for each numerical answer, no partial credit, need to show units.
Total = 4.0
1.
A 60 kg sprinter is running a race on an unbanked circular track with a circumference of 200 m. At the
start, she increases speed at a constant rate of 5 m/s
2
for 2 seconds. After two seconds, she maintains a
constant speed for the duration of the race.
a. How long does it take for her to run the 200 m?
to solve for the time, you need to break the race into two time periods: one with a constant tangential
acceleration of 5 m/s
2
(the first two seconds) and one with a constant tangential acceleration of 0 m/s
2
( after
two seconds have gone by).
Find the distance traveled in the first 2 seconds:
∆
r = v
i
t + 0.5 at
2
= (0)(2) + 0.5(5)(2)
2
= 10 m
After the first two seconds, the runner has (200 m  10 m) = 190 m left to go.
Find the tangential velocity after the 2 seconds of acceleration
v
2 sec
= v
0 sec
+ at = 0 + (5)(2) = 10 m/s
Find the time to complete the remaining distance at this velocity
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This note was uploaded on 02/15/2010 for the course IPHY 4540 at Colorado.
 '09
 KRAM

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