u/Dark_Ghost9487

Hi, my professor assigned me this dynamics problem, but it seems to be wrong because it requires a free-body diagram, and I don't know how to draw one. He also says the result I got is incorrect. Could someone explain why? It's from the book "Engineering Mechanics Dynamics 7th Edition" by J.L. Meriam, from the topic of rigid body kinematics. I've attached an image.