The acceleration due to gravity is  ft/sec/sec.

The initial velocity of object is  ft/sec.

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Acceleration of  a object is rate of change in velocity .

Velocity is .

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Substitute  in .

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The position of a object at time  is .

Velocity of a object is rate of change in position .

Position at time  is  .

Apply derivative on each side with respect to .

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The object reaches maximum height when velocity is zero.

The position of ball when time  is  ft.

 ft.

Substitute  ft.

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The initial velocity is  ft/sec.

The initial velocity is  ft/sec.