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Question
The US athlete Florence Griffith-Joyner won the 100 m sprint gold medal at Seoul Olympics in 1988, setting a new Olympic record of 10⋅54 s. Assume that she achieved her maximum speed in a very short time and then ran the race with that speed till she crossed the line. Take her mass to be 50 kg. Assuming that the track, wind etc. offered an average resistance of one-tenth of her weight, calculate the work done by the resistance during the run.
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Solution
Given:
Distance covered by her, s = 100 m
Time taken by her to cover 100 m, t = 10.54 s
Mass, m = 50 kg
The motion can be assumed to be uniform.
\[\text{ Weight = mg = 490 J } \]
\[\text{ Average resistance force offered, } \]
\[\text{ R } = \frac{\text{ mg } }{10} = 49 \text{ J } \]
\[\text{ So, work done against the resitance force } \]
\[\text{ W = - Rs } = - 49 \times 100\]
\[ \Rightarrow \text{ W = - 4900 J } \]
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