Hi, I have a quick question about projectiles on an inclined plane. Specifically, when the projectile is launched down an inclined plane. Is it not possible to use your choice of sign convention? If the projectile is moving from left to right like so: V ..........V ..............V .............__ V__ Could I not choose the x-direction as increasing from left to right just as easily as increasing from right to left? In the first instance, increasing left to right, the initial velocity and acceleration due to gravity in the x-direction would both be positive, and in the second instance they would both be negative. The trouble is: it only seems to work (I only get the "right" answer) when it's the former, Ux and Ax are +. Why is this the case, does anybody know?