A simple pendulum of length 121 cm takes 11/3 minutes to execute 100 oscillations. Then the time that another simple pendulum of length 81 cm takes to execute the same number of oscillations is

Options

A. 2 minutes
B. 3 minutes
C. 6 minutes
D. 9 minutes

Answer

B

Explanation

`t_(1)=nT_(1)andt_(2)=nT_(2)`
`(t_(2))/(t_(1))=(T_(2))/(T_(1))=sqrt((l_(2))/(l_(1)))=sqrt((81)/(21))`
`(t_(2))/(t_(1))=(9)/(11)`
`therefore t_(2)=(9)/(11)xx(11)/(3)=3` minutes.