Two 0.30 g pith balls are suspended from the same point by threads 37 cm long. (

Question

Two 0.30 g pith balls are suspended from the same point by threads 37 cm long. (Pith is a light insulating material once used to make helmets worn in tropical climates.) When the balls are given equal charges, they come to rest 26 cm apart, see figure. What is the magnitude of the charge on each ball? (Neglect the mass of the thread.)
Answer in C

Two 0.30 g pith balls are suspended from the same point by threads 37 cm long. (Pith is a light insulating material once used to make helmets worn in tropical climates.) When the balls are given equal charges, they come to rest 26 cm apart, see figure. What is the magnitude of the charge on each ball? (Neglect the mass of the thread.) Answer in C

Explanation / Answer

Distance of the center to the mass afterseparation r = x / 2= 13 cm
from figure sin ? = r / L
? = 20.57 degrees
from figure T cos ? = w = mg
from this tension T = mg / cos ?
= [ 30*10 ^ -5 * 9.8 ] / cos 20.57
= 314.02 * 10 ^ -5 N
from figure T sin ? = Fe
from this Fe = 110.3 * 10 ^ -5 N
we know Fe = K q ^ 2 / x ^ 2
where K = couomb's constant = 8.99 * 10 ^ 9 N m ^2/ C ^ 2
from above charge q = x ?[Fe / K ]
= 0.21 m * 3.503 * 10 ^ -7
= 9.1078 * 10 ^ -8 C

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