Question

Sean tossed a coin off a bridge into the stream below. The path of the coin can be represented by the equation 2 h tt = − 16t^2+ 72t+ 100 (where t is time in seconds and h is height in feet) How long will it take the coin to reach the stream?

Answer 1

Answer:

It will take 5.61 seconds for the coin to reach the stream.

Step-by-step explanation:

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

$h(t) = -16t^{2} + 72t + 100$

How long will it take the coin to reach the stream?

The stream is the ground level.

So the coin reaches the stream when h(t) = 0.

$h(t) = -16t^{2} + 72t + 100$

$-16t^{2} + 72t + 100 = 0$

Multiplying by (-1)

$16t^{2} - 72t - 100 = 0$

Solving a quadratic equation:

Given a second order polynomial expressed by the following equation:

$ax^{2} + bx + c, a\neq0$.

This polynomial has roots $x_{1}, x_{2}$ such that $ax^{2} + bx + c = a(x - x_{1})*(x - x_{2})$, given by the following formulas:

$x_{1} = \frac{-b + \sqrt{\bigtriangleup}}{2*a}$

$x_{2} = \frac{-b - \sqrt{\bigtriangleup}}{2*a}$

$\bigtriangleup = b^{2} - 4ac$

In this question:

$16t^{2} - 72t - 100 = 0$

So

$a = 16, b = -72, c = -100$

$\bigtriangleup = (-72)^{2} - 4*16*(-100) = 11584$

$t_{1} = \frac{-(-72) + \sqrt{11584}}{2*16} = 5.61$

$t_{2} = \frac{-(-72) - \sqrt{11584}}{2*16} = -1.11$

Time is a positive measure, so we take the positive value.

It will take 5.61 seconds for the coin to reach the stream.