<i>An exceptional jumper could reach a vertical height of 0.75m. What force must a 75kg person exert to achieve this height? (assume the person crouches 0.30m to jump).</i>(adsbygoogle = window.adsbygoogle || []).push({});

Okay, I know that what I'm going to have to start with:

y = viy * t + 0.5 * g * t^2

to find max height at some velocity...

(.75m-.30m) =d (10m/s^2)= g

.45m = (viy) * t = .5 * g * t^2

Right, so I have no time, but there is:

t = (vi)/g

Hrm, I still don't have (vi) or t...

My next thought is to find maximum PE...

PE = mgh

PE = 75kg * 10m/s^2 * .3m = 225J

So, I know max energy...

Work = force * mass

225J = f * 75kg, f = 500N

So, I know he can push off with a max of 500N

500N = 75kg * a

F = m * a

a = 6.66m/s^2

so I can use

6.66*t= .45m

t=.0676secs

y = viy * t + 0.5 * g * t^2

y = (6.66) * .0676 = .5 * 10 * .0676^2

about .47m, so I'm very close!

F = m * a

F = 75kg * 6.66 =500N + 750N = 1250N required

I know this is wrong, I would appreciate some help

Thanks in advanced!

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# Homework Help: What force must a person exert to jump 75 cm high

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