Question 531205: Problem:
A ball is thrown upward with an initial velocity of 35 meters per second from a cliff that is 30 meters high. The height of the ball is given by the quadratic equation h=-4.9t^2+35t+30 where h is in meters and t in the time in seconds since the ball was thrown, find the time it takes the ball to hit the ground. Round you answer to the nearest tenth of a second.
I understand the the equation is given to you, but I'm not certain how to figure it out. If someone could instruct me on HOW to get the correct answer instead of just giving me the answer, I would appreciate it.
Cheers!
Angela
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! A ball is thrown upward with an initial velocity of 35 meters per second from a cliff that is 30 meters high. The height of the ball is given by the quadratic equation h=-4.9t^2+35t+30 where h is in meters and t in the time in seconds since the ball was thrown, find the time it takes the ball to hit the ground. Round you answer to the nearest tenth of a second.
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h(t) =-4.9t^2+35t+30
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When the ball hits the ground its height is zero.
So, solve -4.9t^2+35t+30 = 0
Use the quadratic formula:
t = [-35 +- sqrt(35^2-4*-4.9*30)]/(2(-4.9))
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t = [-35 +- sqrt(637)]/(-9.8)
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To get a positive solution:
t = [-35-25.24]/(-9.8)
t = 6.15 seconds
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Cheers,
Stan H.
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