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## Homework Statement

A tennis ball has a mass of 0.057 kg. After falling 18 m vertically from rest it has a speed of 12 m/s. What is the magnitude of the average resistive force acting on it as it falls?

My answer for this was .3306N

mass = 0.057kg

Vi = 0 m/s

Vf = 12m/s

Xi = 18m

Xf=0m

I started with w=mg = -0.05586N

So FN must be 0.05586N since it is dropped vertically. The free body diagram would be FN pointed up and weight pointing straight down.

I used the equation V^2 = Vi^2 +2a[tex]\Delta[/tex]x

(12m/s)^2 = 2a(-18m)

a = -4m/s^2

F=ma

F=(.057kg)(-4m/s^2) = -0.228N

Fnet = Fn + Fresistance = .5586N + (-.228N) = .3306N