$12\mathrm{.}17$ A $5000-lb$ truck is being used to lift a $1000-lb$ boulder $B$ that is

$200-lb$ pallet $A.$ Knowing the acceleration of the truck is $1$

determine $($a$)$ the horizontal force between the tires and the gr

$($b$)$ the force between the boulder and the pallet.

Fig. P$12\mathrm{.}17$