A roller-coaster track has six semicircular "dips" with different radii of curvature. The same roller-coaster cart rides through each dip at a different speed.

For the different values given for the radius of curvature R and speed v, rank the magnitude of the force of the roller-coaster track on the cart at the bottom of each dip.
(a) R=15m, v=12m/s
(b) R=30m, v=16m/s
(c) R=60m, v=16m/s
(d) R=45m, v=4m/s
(e) R=15m, v=8m/s
(f) R=30m, v=4m/s

[Solution]
From the formula of centripetal force

Order is (d)>(c)=(f)>(b)>(e)>(a)