A solid cylinder has a mass of

[bww]

A solid cylinder has a mass of 10kg and a radius of .2 meters. Starting from rest it achieves a rotational velocity of 2 revolutions per second after 4 seconds.
a. What torque is required to cause this?
I found the Inertia, (.5)(10(.2) =.2 and found alpha= 2*2pi/4 and got 3.142. Then I took
.2(3.142) to find the Torque of .628Nm.

The problem I encounter is on part b.
B. How long did it take for the cylinder to rotate through its first 2pi radians?
I think it sounds rather basic but the question confuses me. Am I suppose to use the radius of .2 and the 3.142. I really don't know what is wanting me to do.

And then for part c.
C. Assuming this is produced by a string wound around the cylinder, how hard in Newtons, would the string have to be pulled?
I use the Torque formula again right? F*L? so i take like .628 and divide it by .2 to get 3.14N?

Those are my thoughts, great appreciation to anyone who can help me out! Thanks!

 

[Math Jeans]

For part B, what it is asking is how long it takes for the cylinder to rotate one full circle. That is what 2pi radians is.

 

[Shooting Star]

B) Use theta=1/2(alpha*t^2), where theta = 2*3.142. Find t.
C) Torque = Force*radius. What you've written is correct.