# Homework Help: Physics question #2 - tough

1. Feb 17, 2008

### SPH4U

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

Lindsay was on her way to visit her grandmother in Kansas when suddenly a tornado picked her up and transported her to Oz. While standing beside a 198m cliff, she dropped a yellow brick over the side. It has a mass of 1.9Kg. As it was plummeting to the ground, she decided to time the last 50m of its fall. She measured 1.5s on her stop watch. She later impressed the wizard by correctly calculating the gravitational acceleration constant of Oz. What was it?

2. Relevant equations

d = V1t + 0.5(a)(t)^2
d = V2t - 0.5(a)(t)^2

d[total] = 198m
d[timed] = 50m
m[timed] = 1.9Kg
t = 1.5s

3. The attempt at a solution

I tried to use all the equations I know, but I'm always missing one variable to complete it. Could you guys help me out and give me a starting point so I can finish it? Greatly appreciated.

2. Feb 17, 2008

### Staff: Mentor

Fill in the blanks:

First postion: d = ?; time = t
Second position: d = 198 m; time = t + 1.5 s

3. Feb 17, 2008

### SPH4U

Thanks Al, so far, I got this:

d=v1t+0.5(a)(t)^2
198m=(0.5)(a)(t+1.5)^2
198m=(0.5)(a)(t^2+3t+2.25)

Where do you go from there? It looks like I need another hint.

Factoring that quadratic gives me a double zero at -1.5, what does that mean?

I was thinking... 0=(0.5)(a)((2x+3)^2)-198m, but it doesn't make sense.

4. Feb 17, 2008

### Staff: Mentor

That describes the second point. You also need an equation describing the first point.

Then you'll have two equations and two unknowns.