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?