Nuances of 0 J of work in UCM

[SaintJude]

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So a person swings a ball in a horizontal circle above his head such that the ball undergoes uniform circular motion. The tension in the string is 10 N. The work done by the centripetal force is zero because

a.) the object's total displacement is zero
b.) tension is perpendicular to the velocity of the motion

I made this question up! So no need to waste your time on explaining why b is correct. But what I'm wondering is this: Is Choice A also a valid reason or is it technically incorrect?

 

[theseeker4]

So a person swings a ball in a horizontal circle above his head such that the ball undergoes uniform circular motion. The tension in the string is 10 N. The work done by the centripetal force is zero because

a.) the object's total displacement is zero
b.) tension is perpendicular to the velocity of the motion

I made this question up! So no need to waste your time on explaining why b is correct. But what I'm wondering is this: Is Choice A also a valid reason or is it technically incorrect?

A is certainly a true statement (if net displacement is 0, net work is 0)....not sure what more you might be looking for....

 

[SaintJude]

On the MCAT, there can often be a choice that may be 'true statements' but not the REASON for why something is happening. I don't think A is the correct answer b/c the work done by the tension is zero because of explanation in Choice B & is irrelevant to object's displacement in this case.

Anyone agree or disagree?

 

[theseeker4]

On the MCAT, there can often be a choice that may be 'true statements' but not the REASON for why something is happening. I don't think A is the correct answer b/c the work done by the tension is zero because of explanation in Choice B & is irrelevant to object's displacement in this case.

Anyone agree or disagree?

Ah, you asked if it was incorrect, not if it was the best answer. I agree that B would be the best answer for the test.