Question

Two indentical pith balls, each carrying charge q, are suspended from a common point by two strings of equal length l. Find the mass of each ball if the angle between the strings is 2theta in equilibrium.

Answer 1

Explanation:

Let m is the mass of each ball and balls are suspended from a common point by two strings of equal length L, at equilibrium condition angle betwe stings is 2θ as shown in figure.

at equilibrium ,

Tcosθ = mg

And , Tsinθ = Kq²/r² ,where r = 2Lsinθ

∴ Tsinθ/Tcosθ = Kq²/r²mg

⇒tanθ = Kq²/(2Lsinθ)²mg

⇒ m = kq²/{4L²sin²θ × tanθ × g}

l

= Kq²cosθ/4L²sin³θg

Hence, mass of each ball is kq²cosθ/

4L²sin³θg