A 250 gg , 25-cm-diameter plastic disk is spun on

Mary Buchanan

Mary Buchanan

Answered question


A 250 gg , 25-cm-diameter plastic disk is spun on an axle through its center by an electric motor.
What torque must the motor supply to take the disk from 0 to 1800 rpm in 4.3 s ?

Answer & Explanation



Beginner2022-01-15Added 26 answers

Mass of disk, m=250g0,25kg
Diameter of disk, α=25cm0,25m
Initial angular velocity, ωi=0rads
Final angular velocity, ωf=1800RPM
Time, t=4,3s
Angular acceleration , α=ωfωit
Moment of inertia od disk about its centre : I=12mr2
Where r=α2
Using relation: torque, τ=Iα
Mollie Nash

Mollie Nash

Beginner2022-01-16Added 33 answers

The point where the individual fields cancel cannot be in the region between the shells since the shells have opposite-signed charges. It cannot be inside the radius R of one of the shells since there is only one field contribution there (which would not be canceled by another field contribution and thus would not lead to zero net fields). We note shell 2 has a greater magnitude of charge (|σ2|A2) than shell 1, which implies the point is not to the right of shell 2 (any such point would always be closer to the larger charge and thus no possibility for cancellation of equal-magnitude fields could occur). Consequently, the point should be in the region to the left of shell 1 (at a distance r>R1 from its center); this is where the condition
Using the fact that the area of a sphere is A=4πR2, this condition simplifies to :
We note that this value satisfies the requirement r>R1. The answer, then, is that the net field vanishes at x=r=3.3cm.


Skilled2022-01-23Added 488 answers

Thanks for the answers, I got an excellent rating.

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