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A wheel turning with angular speed of 30...

A wheel turning with angular speed of 30 rev / s is brought to rest with a constant acceleration. It turns 60 rev before it stops. The time that elapses before it stops is

A

2s

B

4s

C

5s

D

6s

Text Solution

Verified by Experts

The correct Answer is:
B
`theta= 60 xx 2pi= 120pi` rad
`omega_(0)= 2pi xx 30= 60pi` rad/sec, `omega= 0`
`omega^(2)= omega_(0)^(2) + 2 alpha theta`
`rArr alpha= (-(60pi)^(2))/(2 xx 120pi) = (-60 pi xx 60pi)/(2 xx 120pi)= (-30pi)/(2)= -15pi "rad/sec"^(2)`
`omega= omega_(0) + alpha t`
`rArr t= (- omega_(0))/(alpha)= (-60pi)/(-15pi)= 4` sec
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