1. a fearless 58 kg physics student decides she wants to go bungee jumping from

Question

1. a fearless 58 kg physics student decides she wants to go bungee jumping from a 75 m high bridge above a crocodile infested river. Unfortunately, she must calculate the minimum spring constant for the bungee cord which allow her to complete the jump successfully. Assuming the minimum spring constant is one which allows her to descend the full 75 m (but no more) and the bungee cord does not begin to stretch until she has fallen 15 m, find the minimum value of the spring constant of the bungee cord. hint: it will be best to put h=0 at the height where the bungee cord begins to stretch.

A 3.6 kg mass is released from rest and begins to slide down an 8.0 m long frictionless incline. When the block has slid 5.3 m, a person grabs a cord attached to the mass and begins to pull the cord parallel to the incline. By pulling on the cord, the person is able to slow the mass suclh that it comes to a stop just as it reaches the end of the 8.0 m long incline. Assuming the tension in the cord is constant, find the tension in the cord. 3.6 kg 5.3 m cord 170

Explanation / Answer

Let h = 0 where the bungee cord begins to stretch.

Speed of the person at h = 0 is, v15 = (2 * 9.81 * 15)1/2 = 17.15 m/s

Using principle of conservaation of energy, we know that the total energy at h = 0 is equal to the total energy at h = (75 - 15) m = 60 m

So,

mv152/2 + 0 + 0 = 0 + k*602/2 + mg*(-60)

=> 58 * 17.152/2 = 1800k - (60 * 58 * 9.81)

=> spring constant, k = [(60 * 58 * 9.81) + (58 * 17.152/2)] / 1800 = 23.7 N/m

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