A projectile of mass 1.050 kg is shot straight up with an initial speed of 24.0 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 23.2 m, determine the magnitude of the average force due to air resistance.
We know there is air resistance, so we know that there are non-conservative forces lurking about. Thus
The force due to air resistance (F) is always in the opposite direction of the displacement, so
Call upward positive and set the zero point for the gravitational potential energy at the point where the projectile is shot upward. (Typically I choose the 0 point for GPE at the lowest point in the diagram. That way I don't have to mess around with negative h values.) So , and since the projectile is going to the max height, v = 0 m/s. Also note that in this coordinate system. Thus
You can plug the numbers in.