A small metal ball with positive charge q and mass m is attached to a very light

Question

A small metal ball with positive charge q and mass m is attached to a very light string, as shown in (Figure 1) . A larger metal ball with negative charge ?Q is securely held on a plastic rod to the ceiling. The distance between balls' centers is r.

Write an expression for the magnitude of the force T that the string exerts on the ball. Assume that the values of qand Qare positive.

Express your answer in terms of the variables q, m, Q, r, and appropriate constants.

A small metal ball with positive charge q and mass m is attached to a very light string, as shown in (Figure 1) . A larger metal ball with negative charge ?Q is securely held on a plastic rod to the ceiling. The distance between balls' centers is r.

Write an expression for the magnitude of the force T that the string exerts on the ball. Assume that the values of qand Qare positive.

Express your answer in terms of the variables q, m, Q, r, and appropriate constants.

Explanation / Answer

the upward force= kQq/r^2

downward force = mg+T

as forces are balanced,

mg + T = kQq/r^2

so, T = kQq/r^2 - mg

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