# Homework Help: Equation(s) of motion.

1. Sep 15, 2009

### jewjew

1. The problem statement, all variables and given/known data
A student throws a ball 60 ft into the air

a)How long does he have to wait to catch it on the way down? <----Just needing help on this!
b)What was its initial velocity?<----and this if a) was solved.
c)What will be its final velocity?

2. Relevant equations
x=V(o)T + 1/2(a)T

x = Final Position
V(o) = Initial Velocity
T = Time (assuming final)
a=acceleration

3. The attempt at a solution

Attempt was not full proof but was the only way "I" could think of but I know its wrong.

1st Step: 120 ft. = (0 ft/s)T + 1/2(-32 ft/s^(2))T
2nd Step: 120 ft. = T + (-16ft/s^(2))T ;Zero disappeared. Multiplied 1/2(-16).
3rd Step: (120 ft.)/ (-16 ft/s^(2)) = 2T ; Dividing 120/-16. Added Both Time(T) together.
4th Step: (-7.5 s^(2)) / (2)=T
5th Step: Got -3.75 s^(2) = T

Optional Step: Square root -3.75 s^(2) = Nevermind.....Thats why I need help. Can someone walk me through this. Thank You

2. Sep 15, 2009

### rl.bhat

Check the relevant equation.