Question

A bungee jumper of mass m = 65 kg jumps from a bridge.

A bungee cord with unstretched length L is attached to her leg.
After falling a distance L, the jumper is moving at speed v = 26 m/s and the bungee cord begins stretching and acts like an ideal spring with spring constant k.
Neglect air resistance and the mass of the bungee cord.

Which choice best represents the unstretched length of the bungee cord, L?A. 5.9 m

B. 26 m

C. 34 m

D. 65 m

E. None of these

Answer 1

To solve the problem it is necessary to apply energy conservation.

By definition we know that kinetic energy is equal to potential energy, therefore

PE = KE

`mgh = (1)/(2)mv^2`

Where,

m = mass

g = gravitaty constat

v = velocity

h = height

Re-arrange to find h,

`h=(v^2)/(2g)`

Replacing with our values

`h=(26^2)/(2*9.8)`

`h = 34.498\approx 34.5m`

Therefore the correct answer is C.