A girl throws a tennis ball upward with an initial velocity of 4 m/s. What is the maximum displacement of the ball?

a.) 0.2m up

b.) 0.4m up

c.) 0.8m up

d.) 1.6m up

This is done using the following equations of straight-line motion:

Vf = Vi + a*t

Where: Vf = final velocity

Vi = initial velocity

a = acceleration (in this case, gravity)

t = time

We first have to determine how long it stays in the air on the way up. Substituting the given values and solving for t:

0 = 4 + (-9.8) * t

t = - 4 / - 9.8

t = 0.41s

Using the following equation to solve for displacement, s:

s = Vi * t + 1/2 (a*t^2)

s = 4*0.41 + 1/2 ((-9.8) (0.41^2))

s = 0.81 m

Therefore, the displacement of the ball upwards is 0.8 meters. Among the choices, the correct answer is C.