A physics student with too much free time drops a water melon from the roof of a building. He hears the sound of the watermelon going "splat" 2.50s later. How high is the building? the speed of sound is 340 m/s. Ignore air resistance.
D= Vt (to find how fast sound travels from ground back)
X= Xo + 1/2*(Vo+V)*t
Vf = Vo +a*t
The Attempt at a Solution
So I did everything right except one thing. I calculated the height of the building by finding
y= 340m/s*(2.5-t) *t here being time of the melon hitting the ground. I thought Vf was going to equal -9.8t, found by subbing all known info into the equation Vf = Vo +a*t, it turns out that this portion of information must be positive to get the correct answer though it seems.
When all was said and done I tried to solve the problem for time of fall with,
-4.9t^2 + 340t - 850 = 0, this is not the correct formula though to obtain the correct fall time. I found that it has to be, 4.9t^2 + 340t - 850 = 0.
I just can't logically see why the first term is not negative. In the person's answer I was looking at they had, " -y = -1/2*g*t^2 and that simplifying down to y = 4.9t^2.
I just want to see this problem correctly. I'm learning all this on my own to kind of have a head start next semester. I think it's very important that I get the concepts down in stone and can interpret diagrams with no problem.
Thanks for any help! If you need anymore info I can provide it.