A rod of length L = 20 m and mass m = 50 kg juts out perpendicular to a wall. The rod is designed to pivot vertically about the point where it intersects the wall. A massless pulley is affixed to the wall a height h = 10 m above the rod. A cable is attached to the rod a distance d = h from the wall-rod intersection. The cable slides over the pulley without friction and attaches at the other end to a disk of mass m = 20 kg and radius r = 50 cm on the wall next to the rod. The cable is pulled by turning this disk.
In the first Part of the question, I determined the Tension of the cable to be 693 N.
I Cant figure out the second part of the question:
"If the disk spins at 60 rpm, how long will it take to pivot the rod from horizontal to vertical?"
The Attempt at a Solution
I attempted to Solve for time using w= w0 + at
First I found inertia using the equation: 1/2 mR^2 > I= 2.5
Then I found alpha using: T=a*I=F*r > a= 138.6
I plug these number into the equation (60 rpm = 6.283 rad/s): 6.283= 0 +138.6*t > T=0.04 [/B]
This number for time does not seem possible. What am i doing wrong?