Centripetal Force: Speed Change w/ Doubled Radius & Force

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SUMMARY

The discussion centers on the relationship between centripetal force, radius, and speed in circular motion, specifically when both the centripetal force and radius are doubled. According to the equation F = mv²/r, when substituting 2 for both F and r, the resulting speed increases by a factor of 2, confirming that the correct answer is (B). Participants expressed confusion over the wording of the question and the calculations involved, but the consensus is that the speed does not quadruple as initially suggested by some users.

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brake4country
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Homework Statement


The centripetal force acting on an object is doubled. The radius is also doubled. The speed of the object:

(a) increases by a factor of 4
(b) increases by a factor of 2
(c) decreases by a factor of 2
(d) The change in the object's speed depends on its mass

Homework Equations


F = mv2/r

The Attempt at a Solution


So if I substitute 2's in for F and r in the above equation, my 2's cancel but the correct answer is a. ?
 
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Do a numerical example...
 
brake4country said:
The centripetal force acting on an object is doubled.
So if I substitute 2's in for F and r in the above equation, my 2's cancel but the correct answer is a. ?
Not happy with the wording of the question. Centripetal force does not act. It is the force required to be supplied by forces which do act in order to produce a certain motion.
Anyway, I don't get how the 2's would cancel. (Not that I necessarily agree with the supposed answer.). Please post detailed working.
 
I am sorry; an erroneous math calculation. By substituting 2 for both the force and the radius, I get 4 which is (a). Thank you!
 
Can you still show your calculation ? It doesn't fit at all.
 
brake4country said:
I am sorry; an erroneous math calculation. By substituting 2 for both the force and the radius, I get 4 which is (a). Thank you!
As I hinted, I disagree with that answer. Looks like BvU disagrees with it too.
 
Sorry everyone! That's what happens when you don't read the answer choices correctly! Okay here is the original question: the centripetal force acting on an object is doubled. The radius of the object's motion is also doubled. The speed of the object is:
(A) increases by a factor of
(B) increases by a factor of 2
(C) decreases by a factor of 2
(D) the change in the object's speed depends on its mass.

Fc = mv2/r. If I plug in 2 for F and r, I get 2 = mv2/2 = 4 = mv2. Therefore, the correct answer is (B) increases by a factor of 2! Thanks everyone!
 

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