a disc of mass 20kg and radius 0.5 m is rotating at 8 revolution per second. find torque required to stop after 11 rotation .
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PHYSICS
A uniform disc of mass 20kg and radius 0.5m can tum about a smooth axis through its centre and perpendicular to the disc. A constant torque is applied to the disc for 3s from rest and the angular velocity at the end of that time is
π
240
rev/min. Find the magnitude of the torque. If the torque is then removed and the disc is brought to rest in t seconds by a constant force of 10N applied tangentially at a point on the rim of the disc, find t in seconds.
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ANSWER
Angular impulse = change in angular momentum
∴τt=Iω=
2
1
mR
2
ω.....(i)
∴τ=
2t
mR
2
ω
=
2×3
(20)(0.5)
2
(2π×
π×60
240
)
=
3
20
N.m
During retardation using Eq.(1)
t=
2τ
mR
2
ω
=
2(FR)
mR
2
ω
=
2F
mRω
=
2×10
(20)(0.5)(2π×
π×60
240
)
=4s
Explanation:
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