Resolved: "An exceptional standing jump would raise a person..."

High School
Physics
Force, Motion and Energy
Acceleration Due to Gravity

Ernstfalld

Answered question

2020-12-02

An exceptional standing jump would raise a person 0.80 m off the ground. To do this, what force must a 66-kg person exert against the ground? Assume the person crouches a distance of 0.20 m prior to jumping, and thus the upward force has this distance to act over before he leaves the ground.

Answer & Explanation

pierretteA

Skilled2020-12-03Added 102 answers

Jeffrey Jordon

Expert2021-10-11Added 2605 answers

With most problems dealing with forces and velocities, you can use energy formulas like $E_{k} = E P$ or $W = E_{p}$ or $W = E_{k}$ . Always think of trying an energy formula first; they usually work, and you won't end up doing multiple steps trying to solve for one thing then another thing. With the way you wanted to solve it, you would have to run around solving this and that; it would take a while to get an answer. To use F = ma, you would need to find the initial takeoff velocity using $V_{f}^{2} = V_{i}^{2} + 2 a d$ then solve for Vi since Vf is 0. Then using that as your take off speed you would put that into the same equation $V_{f}^{2} = V_{i}^{2} + 2 a d$ but this time it would be $V_{f} . V_{i}$ would be 0 and 'a' would be what you solve for. The energy method is much much much easier.

work (before) = potential energy (after)

Fd=mgh

$F = \frac{m g h}{d}$
$F = \frac{(66) (9.81) (0.8)}{0.2}$

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