# Kinematics problem help

1. Sep 28, 2008

### Mitchtwitchita

1. The problem statement, all variables and given/known data

A student at a window on the second floor of a dorm sees his physics professor coming along the walkway beside the building. He drops a water balloon from 18.0 m above the ground when the prof is 1.00 m from the point directly beneath the window. If the prof is 180 cm tall and walks at a rate of 0.450 m/s, does the balloon hit his head?

3. The attempt at a solution

Yo = 0
y = -18.0 m + 1.8 m = -16.2 m
g = -9.81 m/s^2
Vo = 0
X = 1.00 m
Vxo = 0.450 m/s

Balloon Drop:

y = yo + Vo*t - 1/2*g*t^2
-16.2 m = 0 + 0 - 1/2(9.81 m/s^2)t^2
t^2 = 16.2 m/4.9 m/s^2
t^2 = 3.31 s^2
therefore, t = sqrt3.31 s^2
= 1.82 s

Professor Walk:

x = Vxo*t
1.00 m = (0.450 m/s)t
t = 1.00 m/(0.450 m/s)
=2.22 s

Therefore, the balloon drops before the professor gets there.

Can anybody please tell me if my attempt is o.k.?

2. Sep 29, 2008

### Kurdt

Staff Emeritus
Re: Kinematics

Looks fine to me.

3. Sep 29, 2008

### Mitchtwitchita

Re: Kinematics

Thanks Kurdt!!