Problema Solution

a rock is prijected directly upward from ground level with an initial volcity of 90 ft / sec. When will the rock be 120 ft above the ground?

Answer provided by our tutors

The equation for the height of the rock is:

h(t) = - 16t^2 + 90t

We need to find such t that h(t) = 120 ft:

- 16t^2 + 90t = 120

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click here to see the equation solved for t

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t1 = 2.17 s

t2 = 3.45 s

The rock will be 120 feet above the ground first time after 2.17 seconds on the way up and second time after 3.45 seconds on the way down.