An athlete pushes against an exercise machine with a force that varies with time

Question

An athlete pushes against an exercise machine with a force that varies with time as shown in the first graph. Also, the velocity of the athlete's arm acting in the same direction as the force varies with time as shown in the second graph. http://session.masteringengineering.com/problemAsset/1528798/5/Hibbler.ch14.p62.jpg -Determine the power applied as a function of time for 0 <= t <=0.2 s Express your answer in terms of t. - Determine the power applied as a function of time for 0.2 <= t <=0.3 s Express your answer in terms of t.

Explanation / Answer

Here F(t) = 800 N.....for 0 <= t <=0.2 s

and F(t) = 800 - 8000*(t - 0.2)... = 2400 - 8000* t.........for 0.2 <= t <=0.3 s

Velocity, v = 20*t / 0.3 for 0 <= t <=0.3 s

So, power = F.v

SO, for 0 <= t <=0.2 s

P = 800 * 20 * t / 0.3 =16000 * t / 0.3 =53333.333 * t...ANSWER

0.2 <= t <=0.3 s

P = [2400 - 8000 * t ]* 20*t / 0.3

=160000 * t - 533333.333 * t^2...ANSWER

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