A heavy flywheel is accelerated (rotationally) by a motor that provides constant

Question

A heavy flywheel is accelerated (rotationally) by a motor that provides constant torque and therefore a constant angular acceleration . The flywheel is assumed to be at rest at time t=0 in Parts A and B of this problem.

a) Find the time t1 it takes to accelerate the flywheel to 1 if the angular acceleration is . Express your answer in terms of 1 and .

b) Find the angle 1 through which the flywheel will have turned during the time it takes for it to accelerate from rest up to angular velocity 1. Express your answer in terms of some or all of the following: 1, , and t1.

c) Assume that the motor has accelerated the wheel up to an angular velocity 1 with angular acceleration in time t1. At this point, the motor is turned off and a brake is applied that decelerates the wheel with a constant angular acceleration of 5. Find t2, the time it will take the wheel to stop after the brake is applied (that is, the time for the wheel to reach zero angular velocity). Express your answer in terms of some or all of the following: 1, , and t1.

Explanation / Answer

a) Apply, w1 = wo + alfa*t1

w1 = 0 + alfa*t

==> t1 = w1/alfa

b) Apply, theta1 = (w1^2 - wo^2)/(2*alfa)

= w1^2/(2*alfa)

c) final angular speed, w2 = 0

use, w2 = w1 - 5*alfa*t2

0 = w1 - 5*alfa*t2

5*alfa*t2 = w1

t2 = w1/(5*alfa)

= (t1*alfa)/(5*alfa)

= t1/5

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