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Help with this Physics Problem!!!! Help!!?
Please help with this problem AND SHOW YOUR WORK PLEASE!
A ball is thrown upward from the ground with an initial velocity of 25.0 m/s; at the same instant, a ball is dropped from a building 15 m high. At what time will the balls be at the same height?
Thanks for the answers,
btw, here's a link to my other physics question - http://answers.yahoo.com/question/index;_ylt=AtVf....
all help is appreciated
2 Answers
- JánošíkLv 78 years agoFavorite Answer
The general equation for height of the balls is:
h = Ho + u×t + a×t²/2
where
h = height
Ho = initial height
u = initial velocity
t = time
a = acceleration by gravity = -9.8 m/s²
The equation for displacement of the upward going ball is:
h = 0 + 25×t + (-9.8)×t²/2
h = 25t - 4.9t²
The equation for displacement of the dropped ball is:
h = 15 + 0×t + (-9.8)×t²/2
h = 15 - 4.9t²
We want the height of both balls to be the same, so
25t - 4.9t² = 15 - 4.9t²
25t = 15
t = 0.6 s < - - - - - - - - - - - - answer
- civil_av8rLv 78 years ago
Same place <--- Equation you need for each ball
At what time <--- Variable you need to solve for
Equation of motion
s = si + vi*t + 1/2*a*t^2
For this problem
h = hi + vi*t - 1/2*g*t^2
Equation for ball being dropped, vi = 0
1) h = hi - 1/2*g*t^2
h = 15 - 4.9 * t^2
Equation for the ball being thrown up... hi = 0
2) h = vi*t - 1/2*g*t^2
h = 25.0 * t - 4.9 * t^2
Since they meet at the same height, set the equations equal and solve for t
15 - 4.9 * t^2 = 25.0 * t - 4.9 * t^2
15 = 25.0 * t
t = 15 / 25 = 0.6 s