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In the animation of the simulation shown below, the RED vectors shown are the forces of reaction *acting on particles A and B* (such as the force on each particle by member AB, and the normal forces of reaction by the floor and wall).

Will this homework set be due Wednesday night or Friday night?

Homework in the course is due on the day of the next regular class period. Since we do not have class on Wednesday, it is due on Friday midnight.

I have two equations: the one for the forces in the x direction for block A and the forces in the y direction for block B. That leaves three unknowns (F_AB, a_A, and a_B).

My first thought was to use the kinematics acceleration equation to write a_A relative to a_B, but that leaves two more unknowns (omega and alpha) for two more equations.

Alternatively, I feel like intuitively, the acceleration of block A in the y direction needs to be matched by an equal acceleration of block B in the x direction, but how would I derive that mathematically?

Please keep in mind that the system is released "from rest" (zero velocity for all components). Therefore omega is known.

The acceleration vector equation adds in two additional equations, with only one additional unknown (alpha). Therefore, you have enough equations to solve for the unknowns.

You do not need to make any assumptions about the relative sizes of the accelerations of A and B. Your equations will give you the answers that you need.

If velocity for all components is zero then omega would be zero, wouldn't that end up making acceleration and angular acceleration all zero?

All we know is that the system is released from rest. In words this means that it is initially held in place (zero velocities and zero accelerations) until it is released. Immediately on release, the forces holding it in place no longer exist, so the system experiences acceleration. The system has not yet moved so it has zero velocity and non-zero acceleration.

A simpler example of release from rest is for you to hold an object in your hand. As you let go of the object, it instantly experiences an acceleration due to gravity. Immediately after release it has not yet developed any speed, yet it has an acceleration.

does it mean there is zero angular velocity?

Yes, all velocity is zero.

Should we be leaving our answer in terms of g? I'm assuming because we weren't given any units to not substitute in 9.81 m/s^2 but I wanted to double check.

That was my thought, since they didn't specify a unit I assume it is better to leave it in terms of g so it's more versatile