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.

1 answer

(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