A person ties a rock to a string and whirls it around in a vertical circle such

Question

A person ties a rock to a string and whirls it around in a vertical circle such that sometimes the rock is going straight upward and sometimes the rock is going straight down. She whirls the rock at the minimum speed (constant in time) such that the string is always taut (no sag). When is the tension the highest? Select one: a. The tension is constant as the rock moves around in a circle. b. It is highest when the rock is at the lowest elevation. c. It is highest when the rock is at the highest elevation A person ties a rock to a string and whirls it around in a vertical circle such that sometimes the rock is going straight upward and sometimes the rock is going straight down. She whirls the rock at the minimum speed (constant in time) such that the string is always taut (no sag). When is the tension the highest? Select one: a. The tension is constant as the rock moves around in a circle. b. It is highest when the rock is at the lowest elevation. c. It is highest when the rock is at the highest elevation Select one: a. The tension is constant as the rock moves around in a circle. b. It is highest when the rock is at the lowest elevation. c. It is highest when the rock is at the highest elevation a. The tension is constant as the rock moves around in a circle. b. It is highest when the rock is at the lowest elevation. c. It is highest when the rock is at the highest elevation

Explanation / Answer

This is a problen regarding circular motion.

Keep in mind that the centripetal force, Fc, will always be changing depending on the force of gravity.

At the highest point, there will be no tension in the string as gravity will provide all of the necessary force towards the center, which is downward.

In between the highest and lowest point, the centripetal force will be some combination of tension and force of gravity.

At the bottom, however, the directions of tension and gravity will be opposite as tention is directed upward toward the center and gravity, ofcouse, is downward. Inorder to keep the rock in motion, the tension has to be greater than gravity. This is, therefore, the position where tension is the highest. So, it is answer choice B.

Hope that helps.

Cheers!

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