I am having a problem with dynamics this semester. Our professor gives us "FE-like" questions, which are actually more complicated than FE questions. I can get to where I need to apply the kinetic energy equation but my units look really large and I don't know what to do with W' or how I can get opposing head wind velocity from that. 1. The problem statement, all variables and given/known data An automobile, weighing 1500 lbf is being driven at 50 mph utilizing 75 hp when it it struck by head wind that drops its speed by 20%. How fast was the wind? Ignore all friction but air drag. 2. Relevant equations F = ma E = (T+V) T = (1/2)mv2 3. The attempt at a solution F = 1500 lbf v1 = 50 mph W' = 75 hp ε = -20% F = ma: 1500 = m(32.17) m = 46.63 sl v2 = v1(1 + ε): v2 = 50(1 - 0.2) v2 = 40 mph 1 = 1.46 fps ∴v1 = 73 fps and v2 = 58.4 fps T1 = (1/2)mv12: T1 = (1/2)(46.63)(732) T1 = T2 = (1/2)mv22: T2 = (1/2)(46.63)(58.42) T2 = The units here don't make sense, since I need to use lbf to get horsepower. Is there a way I can apply force to energy?