# Homework Help: Circlar motion

1. Oct 23, 2009

### xstetsonx

1. A computer disk is 8.0 cm in diameter. A reference dot on the edge of the disk is initially located at θ = +45°. The disk accelerates steadily for second, reaching 1480 rpm, then coasts at steady angular velocity for another second. What are the location and speed of the reference dot at t = 1 s?

2. v=rw

3. i already got the 6.28 m/s for speed. and i thought since i have speed i can just do v=rw to get w and then draw a diagram to get the area under the curve. After i got the area just use delta theta/ 2pi=revolution. then minus the whole number and take the decimal to divide by 360 then plus 45 right? but appreantly i am wrong

2. Oct 24, 2009

### Andrew Mason

We assume it is at rest at t=0 and accelerates until t = 1s at which time its speed $\omege =2960\pi$ rad/sec. To find the angle it covers in that first second, use:

[tex]\theta = \theta_0 + \omega_0t + \frac{1}{2}\alpha t^2[/itex]

AM

Last edited: Oct 24, 2009