5 Two 300 g point charges on 100mlong threads repel each oth

5. Two 3.00 g point charges on 1.00-m-long threads repel each other after being equally charged, as shown in the figure. Calculate the charge. 1.0 m 1.0m/20° i 20 3.0 g 3.0 g

Solution

From Newtons second law

TCos20-mg=0

=>T=mg/Cos20

F_E-Tsin20=0

Since F_E=Kq²/r²

=>Kq²/r²=(mg/Cos20)Sin20 =mgtan20

=>q=r*sqrt[mgtan20/k]

From, figure

r=2*1*sin20 =0.684 m

=>q =0.684*sqrt[3*10^-3*9.8*tan20/(9*10⁹)]

q=7.46*10^-7 C or 746 nC