Question

To jump, you look exert a force of 1400 N of force on the ground. (it exerts 1400 Newtons back onto you) You apply this force over a distance of 0.3 m as you extend your legs. How much work have you done? How high will you rise into the air if your mass is 70 kg?

Answer 1

First, find how stiff your legs are:

$$k=\frac{F}{x}.$$

The work is

$$W=\frac12kx^2=\frac{1}{2}Fx=210\text{ J}.$$

If we spend this work to increase potential energy:

$$W=E_P=mgh,$$

the height will be

$$h=\frac{W}{mg}=0.31\text{ m}.$$