Hello, I am a relatively new member of this website and I wanted to get some help or feedback in helping me understand how to answer these questions. If my format is poor, I am sorry because I just don't know how to use this site that well yet. Anyhow thanks for looking.
A disk with a radius of 0.2 m is initially spinning counterclockwise at a rate of 45 revolutions per minute. At t = 0, a constant angular acceleration of −1.5 rad/s^2 is imparted onto the disk.
a) What is the tangential speed of a point on the outer edge of the disk at t = 2 s?
b) What is the tangential acceleration of a point on the outer edge of the disk at t = 2 s?
ωr = v
a = αr
The Attempt at a Solution
Okay so I started with:[/B]
45 rpm = 45rpm* (2pi/1) = 282.743rad/m
then 282.743rad/m * (1/60 seconds) = 4.71 rad/s
Since I know the radius and angular velocity, I did
4.71rad/s * .2m = .94 m/s
According to the answer my professor gave me, the answer is .34m/s. Can someone please help me explain where I went wrong? Am I suppose to associate t =2 somewhere in my answer?
For the second part, I did something similar, except I used constant acceleration (-1.5/s^2) so it went
-1.5rad/s^2 * .2 = -0.3m/s^2 but the answer was .30m/s^2. Did I do this right?