# Homework Help: AP Physics Problem Set

1. Jan 28, 2016

### master_333

1. The problem statement, all variables and given/known data
Sorry this may be a better picture. I missed the top of the page but the question says

1) In the pole vault event, an athlete runs as fast as possible towards the bar, holding a flexible fiberglass pole. He stick s the end of the pole into a slot in the ground, swings up on the pole and over the bar as shown below (not to scale). Assume the athlete has a mass of 60 kg and his center of mass is 1 m high, relative to the ground. Could you tell me if my steps to part d are correct.

GPE initial - Wfinal = GPEfinal
-Wfinal = GPE final - GPE initial

- 3.5F = 588J - 2646 J
-3.5F = -2058J
F = 588N

My updated answers for question 1 are
1 B) 9.52m/s
1 C) 513 w

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2. Jan 28, 2016

### haruspex

Your answer to B seems a little high. Please post your working.

For d, I do not understand your method for calculating F. Please explain it. What is the 3.5?

Anyway, question d is bad. Average force is defined as $\Delta p/\Delta t$, the change in momentum divided by the time interval. Since you do not know the time taken for the cushion to absorb the impact, there is no way to calculate the average force.
The questioner probably expects you to use $\Delta E/\Delta s$, the change in energy divided by the distance over which the force acted. That gives the right answer when the force is constant, but here it will not be.

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