# Friction Problem

1. Aug 25, 2008

1. The problem statement, all variables and given/known data
A ball starting at h= 9.9 meters slides down a smooth surface where it encounters a rough surface and is brought to rest at B a distance 26.2 meters away. If the ball has a mass of 0.97 kg, to the nearest joule, what is the work done by friction?

Any help to start this problem off?

2. Aug 25, 2008

### Shooting Star

You have not given the complete geometry of the problem. Is the rough surface horizontal?

Anyway, the ball at the top had some property due to its height and that quantity is always conserved, and here it is dissipated totally by friction. That should be enough to answer the question.

As per your request, I'm just trying to start you off.

3. Aug 25, 2008

4. Aug 25, 2008

### Shooting Star

I wouldn't like to give you all the mathematical steps, but you should be able to solve this from whatever hint I am giving you.

When a mass is raised by a height h from some point, it gains some potential energy. When you let it fall back to its original level, this potential energy is converted into kinetic energy due to motion. Here, the ball stops because of friction. So where has all the kinetic energy gone? Has it got anything to do with the frictional force which opposes motion? Try to remember what is meant by "work done" .

5. Aug 25, 2008

### Banaticus

You might have seen the following two equations in class, they might be a good starting point.

<< equations deleted by berkeman >>

For the original poster (OP) -- the equations that Banaticus wants you to think about relate

-1- the relationship between Potential Energy, the mass of an object, and the height to which it is lifted...

-2- the relationship between work done on an object, and the distance through which a force is applied...

Can you write out the two equations that Banaticus is referring to?

Last edited by a moderator: Aug 25, 2008
6. Aug 25, 2008

### Staff: Mentor

Sorry to have to edit your post, Banaticus. Giving the equations outright was a bit too much help. It takes a bit of practice to figure out how to help the OP to do the work themselves -- we definitely appreciate the help here!