Impuls I is given by:
[tex]I = \delta mv = |F|t[/tex]
where [tex]\delta mv[/tex] is the change in momentum, [tex]|F|[/tex] is the average force and t is the time.
Solve the equation for the force F:
[tex]|F| = \frac{\delta mv}{t} = \frac{m(v_f - v_i)}{t}[/tex]
Energy should be conserved, so the velocities will be:
[tex] \frac{1}{2}mv^2 = mgh \\ v = \sqrt{2gh} [/tex]
Combining both equations:
[tex]|F| = \frac{m( \sqrt{2g(h_f + h_i)} )}{t} [/tex]
where [tex]h_f = 30m, h_i = 55m, m = 0.75kg, t = 0.0025s[/tex]
