Pendulum A and B having periodic times 4 s and 4.2 s, are made to oscillate simultaneously. At time t = 0, they are in the same phase. After how many complete oscillations of A, they will be again in the same phase?

Options

A. 7
B. 14
C. 21
D. 28

Answer

C

Explanation

`(T_(2))/(T_(1))=sqrt((g_(1))/(g_(2)))=sqrt((M_(2))/(M_(1))xx((R_(1))/(R_(2)))^(2))=sqrt((1)/(2)xx4)`
`T_(2)=T_(1)sqrt(2)" "2sqrt(2)s`.