# Physics

A wheel with rotational inertia I is mounted on a fixed, fricitonless axle. The angular speed w of the wheel is inccreased from zero to w_f in a time interval T.
1: What is the average net torque on the wheel during the time interval, T?
a) w_f/T
b)w_f/T^2
c) Iw_f^2/T
d)Iw_f/T^2
e)Iw_f/T

I know that torque equals rFsin theda and r=sqrt(I/m). Is the answer e)?

2: What is the average power input to the wheel during this time ineterval T?
a) Iw_f/2T
b_Iw_f^2/2T
c)Iw_f^2/2T^2
d)I^2w_f/2T^2
e)I^2w_f^2/2t^2

what is the equation for power? I don't get this part of the problem... If i had to guess would the answer be b)?

Your reasoning on 1 baffles me. What is avg angular acceleration: wf/T.

Torque= I *angular acceleration

Power? Work= Torque*angular displacement
but angular displacement= 1/2 angacc*time^2

Power= work/time= I*wf/T*1/2*wf/T*T

work it out, and check that.

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1. okay so P=W/t
so the force is the torque from the first problem and you need to find the d
ang. acc. = wf/t
so you use that to plug into the formula: wf^2= wi + 2(alpha)(d)
change wi to zero
and substitue wf/t into alpha and solve for d
use that as the d for Fxd/T and you'll get
Iwf^2/T2

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posted by Teresa
2. We know work is increase or decrease in energy. During this time period the wheel gains kinetic energy K = (1/2)Iwf^2. So that is the work done. power = work/time so the kinetic energy expression over T resulting in Iwf^2/2T

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posted by Cass
3. My girl Teresa out here responding 9 years later

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