An rock is thrown downward from a platform that is 163 feet above ground at 40 feet per second. Use the projectile formula h = − 16 t 2 + v 0 t + h 0 to determine when the rock hit the ground.

The rock hits the ground at t = 4.68 seconds.

Step-by-step explanation:

The height of the rock after t seconds is given by the following equation:

In which v(0) is the initial speed and h(0) is the initial height.

An rock is thrown downward from a platform that is 163 feet above ground at 40 feet per second.

This means that

So

Solving a quadratic equation:

Given a second order polynomial expressed by the following equation:

.

This polynomial has roots such that , given by the following formulas:

When the rock hits the ground?

When h(t) = 0. So

So

Then

Time is a positive measure, then:

The rock hits the ground at t = 4.68 seconds.

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