Question

A circular disc is rotating about its own axis at constant angular acceleration. If its angular velocity increases from 210 rpm to 420 rpm during 21 rotations then the angular acceleration of disc is

Answer 1

final=initial +a*time

average speed=(420+210)/2=315rpm
timefor 21 rotations=21*60/315=4 sec
a= (final-initial)/time= now we need to get units straight, so lets go to rev/sec, and time in sec
a=(420-210)/60 /4 rev/sec^2=210/240=7/8 rev /sec^2

check my math.

Answer 2

210rpm = 210/60 = 3.5 rev/s.
420rpm = 420/60 = 7.0 rev/s.

T1 = 21/3.5 = 6 s.
T2 = 21/7 = 3 s.

V = Vo + a*(T1-T2).
7 = 3.5 + a*(6-3),
a = 1.17 rev/s^2.

7 = 3.5 + a*(6-3).
a = 1.17 rev/s^2.

Answer 3

I want now the clear solution

Answer 4

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