# Homework Help: Advance physics problem

1. Aug 30, 2009

### Leo34005

Velocity Physics Problem

1. The problem statement, all variables and given/known data
Two students are on a balcony 23.4 m above the street. One student throws a ball, b1, vertically downward at 15.5 m/s. At the same instant, the other student throws a ball, b2, vertically upward at the same speed. The second ball just misses the balcony on the way down.

(a) What is the difference in time the balls spend in the air?

(b) What is the velocity of each ball as it strikes the ground?
velocity for b1
velocity for b2

(c) How far apart are the balls 0.480 s after they are thrown?

2. Relevant equations

s = ut + 1/2at
Not to sure

3. The attempt at a solution

I am considering g = 10 m / sec^2.

Motion of the first ball:

=>23.4 = (15.5)t + 10(t^2)/2
=>23.4 = 15.5 t + 5(t^2)
=>(t^2) + 3.1t - 4.68 = 0
=> t = (-3.1 + 5.3) / 2 = 0.6 sec

Motion of the second ball

=>23.4 = - (15.5)t + 10(t^2)/2
=>23.4 = -(15.5 t) + 5(t^2)
=>(t^2) - 3.1t - 4.68 = 0
=> t = (3.1 + 5.3) / 2 = 4.2 sec

Difference in time = 3.6 sec

Last edited: Aug 30, 2009
2. Aug 30, 2009

### Leo34005

Need some help here

3. Aug 30, 2009

### Maroc

Wouldn't your g = 9.8m/s due to gravity ? As for your first question it would be the ball going down, as you throw the ball up it is going against gravity thus making it achieve its goal much slower than the ball going down.

4. Aug 30, 2009

### Leo34005

I think what i did was wrong, and yours too, so can anyone out there help me find the answer? At least i attempted it