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

Spheres and electrostatics

  • Thread starter physicsss
  • Start date
  • #1
319
0
the below figure make small angles theta1 and theta2 with the vertical.

Figure 21-50
(a) If Q1 = Q, Q2 = 3Q, and m1 = m2 = m, determine the ratio theta1 / theta2.

(b) If Q1 = Q, Q2 = 2Q, and m1 = m, and m2 = 4m, determine the ratio of theta 1 / theta 2.

I don't get the forces that are acting on the spheres. I know there's gravitational, electrostatic, and tensional forces. How do I start the problem?
 

Attachments

Answers and Replies

  • #2
The number one thing you have to realize is that the balls are in equilibrium, or, the forces in all directions cancel out.

You have weight vectors pointing down, electrostatic force vectors pointing left and right, and Tension vectors pointing up diagonally. The forces have to cancel out, so just make equations in the horizontal and vertical directions, like [tex]\sum F_{x}=0 , \sum F_{y}=0[/tex].

Hope I helped you out.
 
  • #3
319
0
Don't the electrostatic forces cancel out though since they are the same magnitude and opposite direction?

If that's the case, wouldn't that make tension of the two ropes be the same, and the answer to (a) would just be 1?
 
Last edited:
  • #4
319
0
anyone got an idea?
 
  • #5
551
1
physicsss said:
Don't the electrostatic forces cancel out though since they are the same magnitude and opposite direction?

If that's the case, wouldn't that make tension of the two ropes be the same, and the answer to (a) would just be 1?
The electrostatic forces are the same magnitude and in opposite directions, but they're acting on two different charges! Each charge is in equilibrium and the electrostatic force is balanced by a component of the tension in the string. The tension in each string is not the same, because of the weight of the balls.
 
  • #6
319
0
But for part a), the weight of the balls are the same.
 

Related Threads for: Spheres and electrostatics

  • Last Post
Replies
2
Views
695
Replies
8
Views
4K
Replies
1
Views
986
  • Last Post
Replies
1
Views
4K
  • Last Post
Replies
2
Views
776
  • Last Post
Replies
2
Views
507
Replies
5
Views
3K
Replies
4
Views
2K
Top