Question

A fan makes 2400 rpm. If after it is switched off, it comes to rest in 10 s, then find the number of times it will rotate before it comes to rest after it is switched off.
A. 400
B. 100
C. 200
D. 50

Answer 1

Correct Answer - C
Given, `f=2400"rpm"=(2400)/(60)=40Hz`
`therefore" " omega=2pif=80pi"rad s"^(-2)`
Now, `theta=[(omega_(0)+omega)/(2)]t`
`rArr" theta=[(80pi+0)/(2)]xx10=400pirad`
`therefore` Fan will turn angle `400pi` after it is swtiched off `rArr` The number of rotation `=(theta)/(2pi)=(400pi)/(2pi)=200`