Starting from rest, a fan takes five seconds to attain the maximum speed of 40 rpm(revolutions per minute). Asuming constant acceleration find the time taken by the fan in attaining half the maximum speed.

Explanation

Let the agular acceleratio be `alpha`. According to the question
`400 rev/min=0+alpha5s`………i
Let t be the time taken in attaining the speed of 200 rev/m whilch is half the maximum
Then, `200 rev/min=0+alphat` ………ii
Dividing i by ii we get,
`2=5s/t or t=2.5s`