# Work and Kinetic Energy of weight

1. Jul 24, 2009

### rock_star

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

A 20.0-N weight slides down a rough inclined plane which makes an angle of 30.0o with the horizontal. The weight starts from rest and gains a speed of 15.0 m/s after sliding 150 m. How much work is done against friction? Use g = 10 m/s2.

2. Relevant equations

W = Fd cos θ

3. The attempt at a solution

I substituted it in the equation and got around 2600 J but the answer is wrong.

Can anyone help me out?

Thanks a lot before hand

2. Jul 24, 2009

### rock.freak667

Try using conservation of energy.
150m is the hypotenuse, what is the length of the opposite side of the triangle formed?

3. Jul 24, 2009

### JazzFusion

That's because (for one) you used the wrong force.
a). What force is burning up your mechanical energy: gravity or friction?
b). Stated another way, Which force is non-conservative: gravity or friction?

(Here's a hint: "Work done against friction" = minus "the work done BY friction")