# Help with a Work Problem

1. Sep 29, 2005

### wr1015

After hitting a long fly ball that goes over the right fielder's head and lands in the outfield, the batter decides to keep going past second base and try for third base. The 62.0 kg player begins sliding 2.40 m from the base with a speed of 4.07 m/s. If the player comes to rest at third base, how much work was done on the player by friction?

Any tips on how to set this up??

2. Sep 29, 2005

### Norman

How do you calculate work from a force? Can you find the frictional force from the given information? You are given a mass, try and find an acceleration. You will assume the frictional force is constant in this problem.
Please show us what you have done so far.

3. Sep 29, 2005

### wr1015

sorry bout that, ok i calculated the coefficient of kinetic friction in part a of the problem and it was .352. The acceleration is 3.45 m/s^2.

4. Sep 29, 2005

### Norman

Now that you have the acceleration (or the coefficient of friction) you can figure out the frictional force correct? Now can you get the work done by a constant force from knowing this force and the distance slid?

5. Sep 29, 2005

### wr1015

ok i got the answer and i was doing it right except i wasn't using a negative value for acceleration, but i still don't know how negative work is possible. thanks for the help anyway.

6. Sep 30, 2005

### HallsofIvy

Staff Emeritus
You know the runners mass and velocity just before he slides- and you know that his velocity is 0 when he stops sliding. How much kinetic energy has he lost?

7. Sep 30, 2005

### Norman

HallsofIvy has the easiest way to do this problem, but I that assumes you have done the work-energy theorem.

As for the negative work, it is simply a decision about whether or not the work was done by the object or work was done on the object.

In addition, it is very important that you understand why the minus sign for the acceleration is important. Think about the definition of acceleration and its vector nature.

Cheers,
Ryan