1. The problem statement, all variables and given/known data A speed hump is installed. A 1800 kg car passes over it at 30km/h. The hump follows the arc of a circle with r=20.4 What force does the road exert on the car as the car passes the highest point of the hump? the answer is 1.15x10^4 N according to my professor and this random guy on reddit whose post I found: http://www.reddit.com/r/cheatatmathhomework/comments/l4aji/physics_for_engineers_1/ 2. Relevant equations Force Centripetal = (m*v^2)/r g=9.8 m/s^2 3. The attempt at a solution When the car is at the top of the hump, the force of gravity (mg) is acting towards the center of the circle with radius 20.4 meters, or towards the ground. Therefore, centripetal force and gravity are acting in the same direction. The opposing force, the normal force, must be equal and opposite to keep the car in place. F_net= F(n)-mg-F(c)=0 F(c)= (m*v^2)/r =(1800*8.33333^2)/20.4 =6127.45 mg=17640 F(n)=23767 N But this answer is incorrect according to my professor. Instead, the correct answer comes when F(c) acts in the same direction as the normal force (exactly away from the center of the circle, which defies the definition of centripetal force). F(n)= mg - F(c) =17640 - 6127.45 =11512 which is really close to 11500 which is the answer So my question is, why is centripetal force acting upwards with F(n) and not downwards towards the center of the circle like it should be? Why is centripetal force even a factor in the problem? The car is only accelerating towards the center of the circle (of which the speed hump is a part of) only when it is at the very top. I am very confused. Any help would be great. Thanks.