• Support PF! Buy your school textbooks, materials and every day products Here!

Copper Rod on Two Rails

  • Thread starter tomrja
  • Start date
  • #1
18
0

Homework Statement


A copper rod of mass 0.6 kg rests on two rails 1.3 m apart and carries a current of 31 A from one rail to the other. The coefficient of static friction is 0.3. What is the magnitude of the least magnetic field that would cause the bar to slide?


Homework Equations



F= ILxB

F=ma

f=(Fn)(u) where f is the frictional force, Fn is the normal force, and u is mu.

The Attempt at a Solution



I set up a free body diagram and found the equation: F-(Fn)(u)=ma. In the y direction Fn=mg=(0.6)(9.8)= 5.88N. Then I plugged that into my first equation for the x direction and got F= 0.6a + 5.88. I know that F=ILB, so I plugged that in and solved for B: B= (.6a + 1.764)/40.3. Am I on the right track? If I am then where do I get the acceleration of the copper rod from? Thanks
 

Answers and Replies

  • #2
tiny-tim
Science Advisor
Homework Helper
25,832
250
hi tomrja! :smile:

(have a mu: µ :wink:)
… What is the magnitude of the least magnetic field that would cause the bar to slide?

Am I on the right track? If I am then where do I get the acceleration of the copper rod from?
yes :smile:

and the acceleration is zero

you only need just enough force to get the bar to start moving :wink:
 
  • #3
18
0
hi tomrja! :smile:

(have a mu: µ :wink:)


yes :smile:

and the acceleration is zero

you only need just enough force to get the bar to start moving :wink:
Ahhh duh, guess I should have read the problem again haha. Thanks!!
 
  • #4
gneill
Mentor
20,793
2,773
Just to stir the pot a bit, if the applied force is not horizontally directed it is possible to increase or decrease the normal component of the net force, thus altering the net frictional force. So you might consider finding the optimum angle to apply the force first.
 
  • #5
tiny-tim
Science Advisor
Homework Helper
25,832
250
wow! i never thought of that! :rolleyes:

yes, tomrja, you need to do that also :smile:
 

Related Threads on Copper Rod on Two Rails

  • Last Post
Replies
5
Views
515
Replies
2
Views
4K
Replies
2
Views
3K
Replies
1
Views
229
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
10
Views
12K
Replies
1
Views
2K
Top