Describe how the tension in a bungee cord changes as a rider is dropped, travels downward, reaches the lowest point of the journey, rises back up, and reaches the highest point in the journey.

Question

anonymous · Answer

I  realize that the tension in the cord increases as the rider falls and continues to on the way up as long as the rider accelreates and when the rider begins to slow down while going up the tension deacreases, but Im having difficulty proving this with an FB diagram, because i seem to get FT as a negative while going down. does anyone know how I could make an accurate version of the FBD?

anonymous · Answer

The tension will always point up on a FBD, and the riders weight will always point down. 

The varying tension can shown using Newton's Second Law. $$\sum \vec F_y = ma \rightarrow ma =    F_T - mg$$

As the rider falls the tension is increasing because acceleration is decreasing. Finally, tension reaches it's maximum value, the rider stops and begins to head back up. As the rider travels upwards, the tension decreases as the force of gravity begins to take over.

anonymous · Answer

Oh I see
For some reason I was under the impression that the fram of reference would make Down and right positive
thank you for the answer :)