# Problem of the Day: 1/19/13

A stop sign is cut out of this 2-foot square piece of metal, as shown in the figure below. The side lengths that coincide with the edges of the metal are 1 foot, as not shown in the figure below. How much metal is not used?

Solution to yesterday’s problem:

We are given the initial height i, so our equation becomes $h=-16t^2+3600$. To find the time when $h=0$, let’s substitute in the variable and solve:

$0=-16t^2+3600$

Moving the variable to the other side to handily avoid a negative coefficient, we get

$16t^2=3600$

Taking the square root of both sides,

$4t=60$

Algebraically speaking, it could of course be positive or negative 60; but we can ignore the negative value because there would be no negative time. Finally, we arrive at the solution that the object would hit the ground 15 seconds after dropping.

(Diagrams created with the Isosceles iOS app.)