How Do You Calculate the Charge on Ping Pong Balls in a Coulomb's Law Problem?

[anathema]

I am having a problem with the following question:

Two identically charged ping pong balls each having a mass of 4.00 g are hung from fine threads, 0.75 m long. What is the charge on each ball so that the angle between the threads is 35 degrees?

I don't know how to draw a free body diagram for this problem in such a way that the forces cancel out. Do I just take the vertical component of the gravity and have it cancel with the strictly horizontal electric force, and assume that the vertical component of the gravity is canceled out by the tension of the string? Do I find a way to have both forces acting perpendicularily to the string (and thus tangentially to an arc of motion)?

Thanks in advance.

 

[maverick280857]

Hey you seem to have figured out the problem correctly. The three forces (as you correctly reasoned) are tension, gravity (weight) and the electrostatic force. Gravity always acts vertically downwards, electrostatic force acts horizontally and tension acts at an angle (making 35 degrees with the vertical). So tension has two components...one that balances weight and the other that balances electrostatic force. Now the electrostatic force is that of repulsion not attraction so the horizontal component of tension and the electrostatic force are antiparallel. Draw a diagram now to convince yourself that this is so.

Hope that helps...

Cheers
Vivek

 

[wais]

Hello there,

It seems like you are having trouble visualizing the forces acting on the ping pong balls in this problem. Let's break it down step by step.

First, we need to understand the forces that are acting on the ping pong balls. There are two main forces - the gravitational force, which is pulling the balls downwards towards the ground, and the electric force, which is acting between the two charged balls.

Next, we need to draw a free body diagram for one of the ping pong balls. This means drawing a diagram that shows all the forces acting on the ball. In this case, we can draw a diagram with the gravitational force acting downwards, and the electric force acting towards the other charged ball. The angle between the two forces is 35 degrees, as given in the problem.

Now, we can use Coulomb's Law to find the magnitude of the electric force between the two charged balls. Since the balls are identical, the charges on each ball must be the same. We can set up an equation using Coulomb's Law and solve for the charge on each ball.

As for the tension in the string, it is not necessary to consider it in this problem. The tension in the string will be equal to the weight of the ball, which is already accounted for in the gravitational force.

I hope this helps clarify the problem for you. Remember to always draw a free body diagram and identify the forces acting on the object in order to solve problems involving forces. Good luck!