A roller coaster reaches the top of a hill of radius of curvature 20 m. Riders experience weightlessness. With g≈9.8 m/s², the car speed lies between:
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A roller coaster reaches the top of a hill of radius of curvature 20 m. Riders experience weightlessness. With g≈9.8 m/s², the car speed lies between:

G1 Physics · Accepted Answer

Step 1: At the top, weightlessness means normal reaction N=0. Step 2: Gravity alone provides centripetal force: mg=mv²/R. Step 3: Thus v=√(gR)=√(9.8×20)=14 m/s, at the lower edge of the 14–15 m/s band. Final answer: A — 14 and 15 m/s.