Problem 12.27 Part A Starting from rest, a 12-cm-diameter compact disk takes 2.5
ID: 1796191 • Letter: P
Question
Problem 12.27 Part A Starting from rest, a 12-cm-diameter compact disk takes 2.5 s to reach its operating angular velocity 2500 rpm Assume that the angular acceleration is constant. The disk's moment of inertia is 2.5 x 10 kg m2 How much torque is applied to the disk? Express your answer to two significant figures and include the appropriate units T=( Value Urlits Submit My Answers Give Up Part B How many revolutions does it make before reaching full speed? Express your answer using two significant figures rev Submit My Answers Give Up ContinueExplanation / Answer
w = 2500 rpm = 2500 x 2pi rad / 60 min
w = 261.8 rad/s
Applying wf = w0 + alpha t
261.8 = 0 + alpha x 2.5
alpha = 104.7 rad/s^2
(A) torque = I alpha
= (2.5 x 10^-5) (104.7)
= 2.62 x 10^-3 N m
(B) wf^2 - wi^2 = 2 alpha theta
261.8^2 - 0^2 = 2(104.7) theta
theta = 327.3 rad
revolutions = 327.3 / 2pi = 52 revolutions