Coulombs law not working

  • Thread starter mujadeo
  • Start date
  • #1
103
0

Homework Statement



A rigid, insulating fiber runs along a portion of the y-axis; the fiber isnot free to move. Gravity acts downward (g = 9.81 m/s2).A charge Qa = -7 µC is fixed to the fiber at the origin. A bead with a hole drilled through its center is slipped over the fiber andis free to move along the fiber without friction. The mass of the bead is m = 250g and its charge is Qb. At equilibrium, the bead floats a distanceyb = 11 cm above the origin.


Calculate the charge on the bead.


Homework Equations



Why isn't coulonmbs law working for me????

The Attempt at a Solution



OK heres what i did

F = (KQa * Qb) / r^2

(absolute values for the charges)
(i got F by realizing that it must balance the opposing downward force (drew FBD)

so,

(.245)9.81 = (9.0*10^9) (7*10^-6)Qb / ((.011)^2)


So Qb comes to 4.71*10-9
=wrong for sum reason

Please help and THANKS!
 

Answers and Replies

  • #2
103
0
UPDATE:
i was saying that 11cm = .011m that was prob.

One other question though.
Why does the opposing charge have to be negative??
 

Related Threads on Coulombs law not working

  • Last Post
Replies
2
Views
6K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
10
Views
6K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
1
Views
4K
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
3
Views
2K
Top