Homework Hint: Problem 7/21

Here are some suggestions in solving this problem:

1. Attach observer to the disk. Let xyz be attached to the disk. Let XYZ be a fixed set of axes. (Note that in the above figure I have changed the names of these axes from that given in the text to make these names more consistent with what we have used in lecture.)
2. Note that the above choice of observer sets the omega vector used in the kinematics equations to be that of the disk. Also note that omega_x is about the FIXED axis X, whereas omega_z is about the MOVING axis z.
3. When you differentiate the omega vector to find the alpha vector recall that X is fixed and z is moving.
4. For this choice of observer, both the velocity and acceleration of B as seen by the observer on the disk is ZERO.
5. When using the velocity equation, v_B = v_O + (v_B/O)_rel + omega x r_B/O, note that O is an acceptable point to use since O is attached to the same rigid body as the observer (do you see this?). O is a good point to choose since it has both zero velocity and zero acceleration.
6. Repeat the above for the acceleration of point B.

Let us know if you have any questions.