Question

Disturbed by speeding cars outside his workplace, Nobel laureate Arthur Holly Compton designed a speed bump (called the "Holly hump") and had it installed. Suppose a 1 800-kg car passes over a hump in a roadway that follows the arc of a circle of radius 18.8 m.
a. If the car travels at 33.0 km/h what force does the road exert on the car as the car passes the highest point of the hump?
b. What is the maximum speed the car can have without losing contact with the road as it passes this highest point?

Answer 1

:  30.50 km/h = 30.50^3 m / 3600s = 8.47 m/s 

At the top of the circle the centripetal force (mv²/R) comes from the car's weight (mg) 

So, the net downward force from the car (Fn) = (weight - centripetal force) .. and by reaction this is the upward force provided by the road .. 

Fn = mg - mv²/R 
Fn = m(g - v²/R) .. .. 1800kg (9.80 - 8.47²/20.20) .. .. .. ►Fn = 11 247 N (upwards) 
(b) 
When the car's speed is such that all the weight is needed for the centripetal force .. then the net downward force (Fn), and the reaction from the road, becomes zero. 

ie .. mg = mv²/R .. .. v² = Rg .. .. 20.20m x 9.80 = 198.0(m/s)² 

►v = √198 = 14.0 m/s