Chapter 12.1, Problem 12.69P

A 0.5-kg block B slides without friction inside a slot cut in arm OA that rotates in a vertical plane. The rod has a constant angular acceleration $\ddot{\theta }=10\text{rad}/{\text{s}}^2$. Knowing that when θ = 45° and r = 0.8 m the velocity of the block is zero, determine at this instant, (a) the force exerted on the block by the arm, (b) the relative acceleration of the block with respect to the arm.

Fig. P12.69