Homework Help: Physics boulder problem

1. Aug 26, 2011

iampaul

1. The problem statement, all variables and given/known data
An alert hiker sees a boulder fall from a cliff. He notes that it takes 1.3 sec for the boulder to travel the last third of the fall. a.)Find the height H of the cliff. B.) If you found a quadratic equation of two solutions for a.) what is the relevance of the other one
2. Relevant equations
v2=vo2+2gX
X=vot+0.5gt2
3. The attempt at a solution
v2=vo2+2gX ;vo=0;X=H/3
v2=2(9.8m/s2)(H/3)
v=sqrt(13.07m/s2H)

X=vot+0.5gt2
H/3=sqrt(13.07m/s2H)(1.3s)+8.281m
H=3.9ssqrt(13.07m/s2H)+8.281m
H-3.9ssqrt(13.07m/s2H)-8.281m=0
I just used my calculator to solve this quadratic equation
sqrt(H1)=14.66m0.5
H=214.9 which is the same with the book's answer
sqrt(H2)=-0.56m0.5
H2=0.3136m
I cant answer B.) What is the relevance of H2
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Aug 26, 2011

PeterO

Firstly, were your answer(s) to the first part correct - I don't want to spend time proving you are correct/incorrect.