Yahoo Answers: Answers and Comments for Physics average speed qusetion pls help :)? [Physics]
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From jubby.xo
enUS
Thu, 28 Jan 2010 17:03:50 +0000
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Yahoo Answers: Answers and Comments for Physics average speed qusetion pls help :)? [Physics]
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https://answers.yahoo.com/question/index?qid=20100128170350AATa0xq
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From EM: distance = (rate)(time)
For the first half ...
https://answers.yahoo.com/question/index?qid=20100128170350AATa0xq
https://answers.yahoo.com/question/index?qid=20100128170350AATa0xq
Thu, 28 Jan 2010 19:21:08 +0000
distance = (rate)(time)
For the first half of the trip:
x/2 = (74.0 km/h)(t1)
t1 = x/(2 * 74.0 km/h) [1]
For the second half:
x/2 = (v)(t2)
t2 = x/(2v) [2]
For the whole trip:
x = (85.0 km/h)(t1 + t2) [3]
Adding [1] & [2], substitute into [3], and solve for v:
t1 + t2 = x/(2 * 74.0 km/h) + x/(2v)
x = (85.0 km/h)(x/(2 * 74.0 km/h) + x/(2v))
1 = (85.0 km/h)(1/(2 * 74.0 km/h) + 1/(2v))
1/(85.0 km/h)  1/(2 * 74.0 km/h) = 1/(2v)
(85.0 km/h)(74.0 km/h) / [(2 * 74.0 km/h)  (85.0 km/h)] = v
v = 99.8 km/h