# A force of nine newtons acts perpendicular on a circular disk (i = 3kg m^2) using the included diagram.

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A.) What is the circular disks angular acceleration?

B.) If it starts at rest what is the disks rotational speed after 3 seconds?

C.) How many radians does the disk rotate through at 3 seconds?

D.)What is the disks rotational Kinetic Energy at 3 seconds?

asked Mar 17, 2014

A. Assume that it is an uniform disk so you can find its moment of inertia as $I=\frac12MR^2$.
Then the angular acceleration $\alpha$ can be found with $I\alpha=\tau$, where $\tau=FRsin(\theta)$ is the net torque applied -- here the angle between the force and R is 90 degree so $sin(90^\circ)=1$.
B. $\omega_f-\omega_i=\alpha\Delta t$, with initial angular velocity being zero.
C. $\theta_f-\theta_i=\omega_i\Delta t+\frac12\alpha\Delta t^2$.
D. $KE_{rot}=\frac12I\omega^2$.