本题目来源于试卷: Space Time & Motion A.2 Forces & Momentum，类别为 IB物理学
[单选题]
A roller coaster pass t -9db n0h l/p/erowl/e pu he /6b(os b45.rdeus a vertical loop in a constant gravitational field. Friction and air resistance are negligib .eo(u 5bed u4s6/br hple.
How do the kinetic energy of the roller coaster and the normal reaction force acting on the roller coaster compare at point X and Y?
A. kinetic energy is greater at X than Y; normal reaction force is greater at Y than X
B. kinetic energy is greater at Y than X; normal reaction force is greater at X than Y
C. kinetic energy is greater at Y than X; normal reaction force is greater at Y than X
D. kinetic energy is greater at X than Y; normal reaction force is greater at X than Y
参考答案: D
本题详细解析:
Explanation:
By conservation of energy, the roller coaster has greater kinetic energy at the bottom of the loop (X), then kinetic energy is converted to gravitational potential energy at the top of the loop (Y). Hence B and C are rejected.
The normal reaction force by the track contributes to the centripetal force needed for the roller coaster to move along the loop. Since centripetal force increases with speed, the normal reaction force is larger at the bottom of the loop (X), when speed is greater. At the bottom of the loop, the normal reaction force is also the sum of the centripetal force and the weight of the roller coaster, while at the top of the loop the centripetal force is normal force is equal to the centripetal force minus the gravitational force.
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