SOLUTION: Please help. Thankyou. A girl throws a ball vertically upward with a speed of 6.10 m/s from the roof of a building 18.29m high. a.) How long will it take the ball to reach the gro

Algebra ->  Customizable Word Problem Solvers  -> Misc -> SOLUTION: Please help. Thankyou. A girl throws a ball vertically upward with a speed of 6.10 m/s from the roof of a building 18.29m high. a.) How long will it take the ball to reach the gro      Log On

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Question 1123912: Please help. Thankyou.
A girl throws a ball vertically upward with a speed of 6.10 m/s from the roof of a building 18.29m high. a.) How long will it take the ball to reach the ground? b.) What will its speed be when it reaches the ground?
Answer by Alan3354(69443) About Me  (Show Source):
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A girl throws a ball vertically upward with a speed of 6.10 m/s from the roof of a building 18.29m high. a.) How long will it take the ball to reach the ground? b.) What will its speed be when it reaches the ground?
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You didn't supply the equation or function for the ball's position.
9.8 m/sec/sec is commonly used on Earth in metric units. Sometimes
10 m/sec/sec is used.
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9.8 is closer to reality.
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h(t) = -4.9t^2 + vo*t + h where vo is the upward speed at launch (not velocity) and h is the launch height.
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a.) How long will it take the ball to reach the ground?
h(t) = -4.9t^2 + vo*t + h
h(t) = -4.9t^2 + 6.1*t + 18.29
-4.9t^2 + 6.1*t + 18.29 = 0 at impact
Solve for t (ignore the negative solution).
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b.) What will its speed be when it reaches the ground?
Speed is the 1st derivative of position.
h'(t) = -9.8t + 6.1
Use the value for t from part a.