1. The problem statement, all variables and given/known data How great a speed can the car in sample 1.6 (with 2.64 axle ratio) maintain when going up a continuous 10 percent grade (1-ft rise in 10-ft horizontal travel)? without the incline the top speed is 117 mi/hr, giving the wheel 1513 rpm (calculated in the example) radius of wheel = 13in 2. Relevant equations at 4000rpm (engine speed): engine output = 160hp W = FV 3. The attempt at a solution because of the rise, the road gives a normal force of 398 lbs in the horizontal direction first i converted everything to standard units. then i found the force required to push the vehicle 117mph with 160hp: F = W/V = 512.9 lb then added the additional force due to the incline: F1 = 512.9 + 398 = 910.9 lb then i solved for the new velocity: V = W/F1 = (convert) = 65.9 mph however the answer is supposed to be 72 mph. where was the mistake?