Solving for Torque, Angular Momentum, and Acceleration in Rotational Motion

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The discussion revolves around solving a rotational motion problem involving a wheel slowing down due to an applied tool. Key calculations include determining the torque exerted, the change in angular momentum, and both tangential and radial accelerations. Initial mistakes were made in converting angular velocities from RPM to radians per second, leading to incorrect answers. After receiving feedback, the poster corrected the conversions and successfully found the right answers for all parts of the homework. The experience highlights the importance of accurate unit conversions in physics problems.
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Homework Statement


A wheel (mass 9.6 kg, radius 0.855 m) in the shape of a disk is rotating at 81.9 rpm when a tool is pressed against the edge of the wheel, slowing it down at a constant rate to 48 rpm in 3.81 seconds. Find:

a) the magnitude of the torque exerted by the tool on the wheel
b) the magnitude of the change in the angular momentum of the wheel during the time the wheel was slowing down
c) the magnitude of the tangential acceleration of the wheel as it slowed down
d) the magnitude of the radial acceleration of a point on the edge of the wheel at the end of the 3.81 seconds

Homework Equations


I =0.5mr^2 = 0.5(9.6)(0.855^2) = 3.51
omega initial = rpm(initial) * 2pi = 514.59
omega final = rpm(final) * 2pi = 301.59
alpha = change in omega / change in time = -55.91

The Attempt at a Solution


(A) tau = I alpha = -196.24

(B) L final = I omega(final) = 1806.211
L initial = I omega(initial) = 1058.581
change in L = -747.63

(C) a(tan) = r alpha = -47.8

(D) a(rad) = r (omega^2) = 77,767.83

These were the formulas the professor gave us, then he threw us with a question like this. The questions are on WebAssign, so I already know these four solutions are wrong. I still have a few chances before I'm locked out of the questions, but i cannot figure out for the life of me how to solve them.
 
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Your angular velocities are 60-times too large. ;)
 
angel120 said:
omega initial = rpm(initial) * 2pi = 514.59
omega final = rpm(final) * 2pi = 301.59
Redo these conversions. rpm = revolutions per minute; you need radians per second.
 
Thanks guys, I feel really dumb making these silly mistakes. Live and learn, eh?

While waiting for a reply, I managed to figure out the right answers for all four parts.

Thanks again, guys. :)
 
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