Concept explainers
You are riding on a Ferris wheel that is rotating with constant speed. The car in which you are riding always maintains its correct upward orientation; it does not invert. (i) What is the direction of the normal force on you from the seat when you are at the top of the wheel? (a) upward (b) downward (c) impossible to determine (ii) From the same choices, what is the direction of the net force on you when you are at the top of the wheel?
(i)
The direction of the normal force on the rider from the seat while at the top of the wheel.
Answer to Problem 6.1QQ
Option (a).
Explanation of Solution
The car always maintains its upward orientation at all points on the ride and it is doesn’t invert its orientation.
Normal force is a kind of contact force and it is always perpendicular to the surface that applies the force. At the top of the wheel, the surface of the seat is horizontal and the rider is on top of it. Hence the normal force on the rider is perpendicular to the seat and upwards.
Conclusion:
Normal force is always perpendicular to the surface of contact. Hence, Option (a) is correct.
Only if the car is inverted, the normal force is downwards. Hence, Option (b) is not correct.
The normal force is always upward. Its means it can be possible to determine. Hence, Option (c) is not correct.
(ii)
The direction of the net force on the rider when he is at the top of the wheel.
Answer to Problem 6.1QQ
Option (b).
Explanation of Solution
Since the car is in circular motion it experiences a centripetal acceleration. Centripetal acceleration is always pointing towards the center.
The net force is equal to the difference between gravitational force and the centripetal force of the wheel. Gravitational force is always vertically downwards and centripetal force always points towards the center.
At the top of the wheel, both the gravitational force and the centripetal force is downwards and hence the resultant force will also be downwards.
Conclusion:
At the top of the wheel, since both gravitational and centripetal forces are directed downwards, net force is also downwards. Hence, Option (b) is correct.
Only at the bottom of the wheel, the centripetal force is upwards and the net force has a possibility to be pointed upwards. Hence, Option (a) is not correct.
Anywhere except the top of the wheel, we need the magnitude of the gravitational and centripetal forces to determine the direction of the net force. But at the top of the wheel, both are in the same direction and hence the direction of the net force can be determined. Hence, Option (c) is not correct.
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Chapter 6 Solutions
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