Answer
Please see the work below.
Work Step by Step
(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
$F=ma=\frac{mv^2}{2\Delta x}$
