Centripetal force

  • #1

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. ???
 

Answers and Replies

  • #2
BvU
Science Advisor
Homework Helper
14,274
3,633
Do a numerical example....
 
  • #3
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
2020 Award
35,909
6,641
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.
 
  • #4
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!
 
  • #5
BvU
Science Advisor
Homework Helper
14,274
3,633
Can you still show your calculation ? It doesn't fit at all.
 
  • #6
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
2020 Award
35,909
6,641
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.
 
  • #7
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!
 

Related Threads on Centripetal force

  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
10
Views
2K
  • Last Post
Replies
10
Views
3K
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
3
Views
2K
Top