The car of a wheel rotating with centain angular velocity is topped in 5 s and before it stops, it makes 20 revolutions . Then initially it was rotating with the frequency.

Options

A. 8Hz
B. 11Hz
C. 12Hz
D. 15Hz

Answer

A

Explanation

Given ,t =5s and n =20`thereforetheta=2pin`
We have `omega=omega_0+alphat`
`alpha =(-omega_0)/(s)" "(because omega=0)`
`omega^2=omega_0^2+2alphatheta`
`rArr omega_0^2=-2alphatheta`
`rArr omega_0^2=2(omega_0)/(5).40pi`
`omega_0=16pi`
`2pin=-16pi" "because omega=2pin`
`therefore " "n=8Hz`