Physics
posted by Sejul .
A projectile of mass 1.350 kg is shot straight up with an initial speed of 22.0 m/s.
(a) How high would it go if there were no air friction?
(b) If the projectile rises to a maximum height of only 17.8 m, determine the magnitude of the average force due to air resistance.
I got the "a" correct with 24.69 m
I need help with part B. I used
F(17.8) = 1/2 (1.350)(22.0)^2 = 18.35 N and it was wrong. I need help with the correct equation to use. Thank you.

(Avg. resistance force) x distance = LOSS of energy, not the initial kinetic energy
Energy loss = Initial KE  M*g*17.8m
= 326.7 J  235.5 J = 91.2 J
Fav = 5.1 N