I'm having trouble with the following problem: "There is a car ready to go down a hill. The height of the hill is 9.0 m, and the length of the slope is 11.0 m (hypotenuse). The frictional force opposing the car is 125 N, and the car must be going 12.5 m/s when it reaches the bottom. What is the initial speed required for the car to overcome friction and reach required speed at the bottom of the hill?" I set up the following equation: KE_i + PE_i + (frictional force)(cos 180)(11.0 m) = KE_f I don't know if I have the right setup because whenever I try to solve it, I run into trouble because there is no mass provided and I get an answer to be around 50 (it should be a little less than 3 m/s).