Question

A 54.0-cm diameter disk rotates with a constant angular acceleration of 2.0 rad/s2. It starts from rest at t = 0, and a line drawn from the center of the disk to a point P on the rim of the disk makes an angle of 57.3° with the positive x-axis at this time.

Find the position of P (in degrees, with respect to the positive x-axis) at t = 2.30s.

The "answer" is suppose to be 0.#### but I keep getting in the hundreds when I convert to degrees from radians.

I've been doing (6.9 rad/s)(2.3s) = 15.87 rad
since 57.3° = 1 radian I did 15.87 - 1 = 14.87 then minus 2(2pi) = 3.303629 then times 180/pi = 131.988°

2nd method is going clockwise so I did 15.87 rad + 1 = 16.87 - 2(2pi) = 4.273629 times 180/pi = 244.8609°

But neither answer is correct since it's suppose to be like in the 0.### area.

Please help!

Answer 1

A = 2(180/pi) = 114.59 deg.
a = 114.59 deg/s^2.

d = Vo + 0.5at^2
d = 0 + 0.5*(114.59)(2.3)^2=303.09 deg.
303.09 + 57.3 = 360.39 deg.

P = 360.39 - 360 = 0.39 deg, CCW from x-axis.