# Homework Help: Incline Problem

1. Jul 12, 2006

### webren

"A block is given an initial velocity of 5.00 m/s up a frictionless 20.0(degrees) incline. How far up the incline does the block slide before coming to a rest?"

The book gives a clue stating that mgx = -mgsin20.0 and mgy=-mgcos20.

My question is why is mgx negative mgsin20?

When I work it out:

Sum of x force = mgsin20 = ma,
therefore: a = gsin20

Do they make it negative because the force of gravity in the x direction is going in a negative direction while the velocity is going in a positive direction?

2. Jul 12, 2006

### LENIN

I think it's negative becouse they defined the the direction of the initial velocity as positive, and so becous it's slowing down (along both the x and the y axis) the accelaration and force have to be negative.

3. Jul 12, 2006

### Cyrus

What course are you taking? I'll be in the Clark building tomorrow. Taking my final exam :yuck:

Ans. Because gravity slows the block down as it slides up the incline.

The correct spelling is "because" lenin. Nice name BTW, clever.

4. Jul 12, 2006

### LENIN

Thank you.

5. Jul 12, 2006

### Cyrus

:rofl: I just noticed your red text, how appropriate,.......commie.

6. Jul 12, 2006