# Finding the radius of a pendulum

1. Oct 17, 2016

### Jrlinton

1. The problem statement, all variables and given/known data
A monkey is swinging a coconut of 1 k in a pendulum like motion. When the monkey's motion is at the bottom of its swing it is .6 m above the ground. He releases the coconut when it it is in this position when the force is 250 N and it travels 10 meters before hitting the ground. What is the length of the monkey's arm?

2. Relevant equations

3. The attempt at a solution
So first is to find the velocity of the coconut, which I need to find the time of flight first. -0.6m=-.5(9.81(t^2) and got t to equal .350 seconds. To find the velocity used 10m=V(.350) with V=28.57m/s.

250N=1kg*(28.57^2/r)
r=3.27m
So the monkey's arm is 3.27 m long?

2. Oct 18, 2016

### ehild

Your solution is correct, (edit: if 250 N is the net force acting on the coconut). It must be a giant monkey

Last edited: Oct 18, 2016
3. Oct 18, 2016

### haruspex

I make it even longer. I assume the 250N is the tension in the monkey's arm at the point of release. What are all the forces acting on the coconut at that point?