Bungee jumping and energy transfers

Question

On the sheet I have it shows a diagram of a bungee jumper at three different positions: waiting to jump (position 1), at E point where the bungee rope is fully unwound and about to start stretching (position 2), and at the lowest point before he rebounds (position 3) Questions

A) which position has the largest gravitational potential energy store? Explain

B) which of the three positions is the bungee jumpers gravitational potential store smallest?explain

C) which position is the ropes elastic energy store largest? Explain

D) explain, in terms of energy transfer why a bungee jumper eventaully will stop moving 

E) describe and explain the changes in the rope's elastic energy store as the jumper moves from position 1 to position 2.

 

I think that question a would be position 1 because it's higher up. Then question b would be 3 as its closest to the ground and c position 2 but i dont know how to explain it. Question D I don't have clue. question e I think it starts as a gravitional energy store then to a elastic energy store transfered to Kintetic energy 

Answer 1

Emma,

 

Your answers are correct for A and B.

 

For C, the rope is stretched the most in order to have maximum elastic potential energy.  This occurs at the bottom of the drop, when the rope is stretched to the max, the speed of the jumper drops to zero, and the jumper is about to start going back up as the rope begins to unstretch itself.

 

For D, there is an interchange of elastic potential energy of the rope with gravitational potential energy, but there is also air resistance, which removes energy from the system, and maybe energy being lost as sound when the rope stretches and unstretches.  Energy is not conserved and eventually the air resistance and other causes of energy dissipation will slow the jumper until a state of static equilibrium is reached between the tension of the rope and the jumper's weight.

 

For E, the rope's elastic potential energy is zero starting at the top, since the rope is not yet stretched, and remains zero until it is fully unwound at position 2, then starts to rise after position 2 and attains its maximum value when it is fully stretched at the bottom, which is position 3.

Answer 2

Hi Emma!

 

Thinks of the bungee cord as a spring.  As with any spring, the more you stretch (or compress) it from its normal length, the more spring potential energy it stores.  So the bungee cord will store the most elastic (spring) potential energy when it is stretched the most.

 

I think you are right on about A) and B), and then use the paragraph above to take another look at C).  For D), I think you could actually use your answer to E), but in a different order for two of them.  The bungee cord stores no elastic energy until it is stretched.  This may help you with both D) and E).

 

I hope that helps!  Just let me know if you want to talk more about it.