Solving the Problem of a Block Sliding Up an Inclined Plane

[webren]

I have a question about this problem:

"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?

 

[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.

 

[Cyrus]

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

Whats your major?

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

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

 

[LENIN]

Thank you.

 

[Cyrus]

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

 

[webren]

Ah, both of your answers make sense. Thank you.

The class I am taking is Engineering Physics I.
I am a computer science major.

Looks like cyrusabdollahi and I go to the same school. Nifty.