Essential University Physics: Volume 1 (3rd Edition)

(a) We know that $a=\frac{v}{\Delta t}$ Hence, the force is given as $F=ma=\frac{mv}{\Delta t}$ (b) We know that the acceleration is given as $a=\frac{v^2}{2\Delta x}$ Hence, the force is given as $F=ma=\frac{mv^2}{2\Delta x}$