In a cartoon program, Peter tosses his baby, Stewie, up into the air to keep the child entertained. Stewie reaches a maximum height of 0.787 m above the release point. Suppose the positive y axis points upward.

Question

(a) With what initial velocity was Stewie thrown? (Express your answer in vector form.)

Answer 1

v = Vi - g t
h =Hi +Vi t - (1/2) g t^2
if g = 9.81 m/s^2
v = 0 at top
9.81 t = Vi so t = Vi / 9.81
Hi = 0
0.787 = Vi t - 4.9 t^2 = Vi^2 /9.81 - 4.9 Vi^2/9.81*2 = Vi^2/19.6
Vi = 3.93 m/s upward

Answer 2

or, if you want another formula, the max height
h = v^2 / 2g
0.787 = v^2/19.62
v^2 = 15.44
v = 3.93

you may already have seen this as relates to the usual horizontal mostion
v^2 = 2as