Question

During one heat of a swim meet, a swimmer performs the crawl stroke in a pool 50.0 mm long She swims a length at racing speed, taking 20.0 s to cover the length of the pool. She then takes twice that time to swim casually back to her starting point. Find (a) her average velocity for each length and (b) her average velocity for the entire swim. If the swimmer could cross a 28 km channel maintaining the same average velocity as for the first 50 mm in the pool, how long would it take?

Answer 1

a)
i)
Total time taken during the race, t = 20 s
Total distance covered, d = 50 m
Average speed, v = d/t
= 50/20
= 2.5 m/s
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ii)
Total time taken during the swim to the starting point, t' = 2 * 20 = 40 s
Total distance covered, d = 50 m
Average speed = d/t'
= 50/40
= 1.25 m/s
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b)
i)
Total distance covered during the entire swim, D = 2d =
= 2 * 50 = 100 m
Total time taken, T = t + t'
= 20 + 40 = 60 s

Average speed = D/T
= 100 / 60
= 1.67 m/s
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ii)
Average velocity in the first 50 m swim, v = 2.5 m/s
Total distance needed to cover, D = 28 km = 28000 m
Time needed = D/v
= 28000/2.5
= 11200 s
= 11200/60 = 186.7 min
= 186.7/60 = 3.1 hr
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NOTE: In the question, the length of the pool is given as 50 mm, but I have taken it as 50 m. If there is any issues, please mention it in the comment box.