# Homework Help: Change in Potential Energy: What am I doing wrong?

1. Oct 2, 2007

### Fittleroni

1. The problem statement, all variables and given/known data
A 4.20 kg block is set into motion up an inclined plane with an initial speed of v0 = 7.70 m/s (Fig. P7.25). The block comes to rest after traveling 3.00 m along the plane, which is inclined at an angle of 30.0° to the horizontal.

1. For this motion, determine the change in the block's kinetic energy.
DeltaK = 1/2m(vf^2-vi^2)^2=-1/2mvi^2= -124.5J

This next question is the portion I am having problems with:

2. For this motion, determine the change in potential energy of the block-Earth system.

2. Relevant equations

DeltaU = mg(3.00)sin30.0

3. The attempt at a solution

=(4.20)(9.8)(3.00)(0.454)
=56.1

So what is wrong with my answer??

2. Oct 2, 2007

### Staff: Mentor

What's the sine of 30 degrees?

3. Oct 2, 2007

### dynamicsolo

Before you begin calculations involving trig functions, always check the mode your calculator has been left in. The sine of 30 grads is 0.454; you need to reset the input mode to degrees...