Kinematics

Mar 2020
2
0
Australia
Hi
I am getting a different answer to my teachers example, the colorful image is the example and the pencil one are my working. i would really appreciate someones input.
the question: A stone is dropped from a hot air balloon that is falling at a constant rate of 5ms. at the instant the stone is dropped, the balloon is 100m above the ground.
A: how long will the stone take to reach the ground?
B: where will the balloon be when the stone hits the ground?

IMG_5730.jpg
 

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topsquark

Math Team
May 2013
2,532
1,051
The Astral plane
I can't read your answer very well, but it looks like we agree. I get t = 4.0361 s.

-Dan
 

skeeter

Math Team
Jul 2011
3,363
1,854
Texas
part a.

$\Delta y = v_{yo}t - \dfrac{1}{2}gt^2$

$-100 = -5t - 4.9t^2$

$t=\dfrac{-(-5) + \sqrt{(-5)^2-4(-4.9)(100)}}{2(-4.9)} = -5.06$

$t = \dfrac{-(-5) - \sqrt{(-5)^2 -(-4.9)(100)}}{2(-4.9)} = 4.04$

the positive solution is correct
 
Mar 2020
2
0
Australia
Thank you very much, i wasnt using the brackets inside of the square root symbol.
 
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