A roller coaster car is at the top of a vertical circular loop of radius 20 m. What minimum speed must the car have at the top of the loop to maintain contact with the track?

Core Concept

At the top of the loop, the centripetal force is provided by gravity and the normal force from the track. To maintain contact, the normal force must be ≥ 0. The minimum speed occurs when N = 0, so mg = mv²/r, giving v = √(gr) = √(9.8×20) ≈ 14 m/s. Option A is incorrect as it's half the required speed. Option C is incorrect as it's √2 times the required speed. Option D is incorrect as it's double the required speed.