$12\mathrm{.}128$ A robot arm moves in the vertical plane so that the $0\mathrm{.}1-kg$ cylinder $P$

travels in a circle about point $B,$ which is not moving. Knowing that

arm $BP$ starts from rest in a horizontal position, and that the speed of

$P$ increases at a constant rate of $200m\frac{m}{s^2},$ determine the force act$-$

ing on the cylinder at $t=3s.$