A ball is thrown vertically upward from the ground Its dista

A ball is thrown vertically upward from the ground. Its distance in feet from the ground in t seconds is s = -16t^2 + 224t. After how many seconds will the ball be 720 feet from the ground? seconds (Use a comma to separate answers as needed.)

Solution

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Given

s = -16t^2 + 224t

Given s = 720 feet

=>

720 = -16t^2 + 224t

16t^2 - 224t + 720 = 0

Dividing the equation by 16 we get

t^2 - 14t + 45 = 0

t^2 - 9t - 5t + 45 = 0

(t-9)(t-5) = 0

t = 5 seconds and 9 seconds.

Kindly note that ball will be at a height of 720 feet after 5th and 9th second of being thrown. (One while going up and other while descending down)

Solution