# Homework Help: Question on total moment of inertia

1. Nov 25, 2009

### chess10771

1. The problem statement, all variables and given/known data

A lawn sprinkler has three spouts that spray water, each r = 15.5 cm long. As the water is sprayed, the sprinkler turns around in a circle. The sprinkler has a total moment of inertia of 9.10 10^-2 kg · m2. If the sprinkler starts from rest and takes 2.60 s to reach its final speed of 3.0 rev/s, what force does each spout exert on the sprinkler?

2. Relevant equations
I= N * M * R ^2, not sure about N

3. The attempt at a solution
The radius is .155 m, I = 9.10 * 10^-2 , I can't figure out how to get M, do i use the fact that it takes "takes 2.60 s to reach its final speed of 3.0 rev/s" , please lay it out for me , thanks

2. Nov 25, 2009

### minger

You have a speed and a time, which means you can calculate acceleration. You're also given a moment of inertia, which means you can find something else useful.

Then given that other useful piece of information, you should be able to find your answer.