$12\mathrm{.}72$ A $700-kg$ horse A lifts a $50-kg$ hay bale $B$ as shown. At the

instant when $r=8m$ and $=60,$ the velocity and acceleration of the

horse are $2\frac{m}{s}$ to the right and $0\mathrm{.}5\frac{m}{s^2}$ to the left, respectively.

Neglecting the mass of the pulley, determine at that instant $(a)$ the tension

in the cable, $(b)$ the average horizontal force between the ground and the

horse's feet.

Fig. P$12\mathrm{.}72$