You need to use trigonometry to work this one out. The components of the force are needed. it is a vector, so work out the unbalanced force using trig. you know that the force pulling the 5kg skateboard down is going to be 9.8 * 5 = 49N. As you have the angle it is on, and 49 is the vertical component, you can use Sin(X) = Op/Hyp where x= 15 degress, the opposite is the vertical component (49N) and the hyp is the unbalanced force - which is 79.35. I think. Somebody plz double check me on that one though :P
