Question

An explosives company specializes in bringing down old buildings. The time it takes for a particular piece of flying debris to fall to the ground can be modelled by the function h left parenthesis t right parenthesis equals negative 18 t squared plus 72 t plus 378, where h is the height of the debris, in metres, and t is the time, in seconds.

How long will it take for the piece of debris to hit the ground after an explosion?

Answer 1

h(t) = - 18 t² + 72 t + 378

The piece of debris hit the ground when h = 0

h(t) = - 18 t² + 72 t + 378 = 0

Now you must solve equation:

- 18 t² + 72 t + 378 = 0

The solutions are:

t = - 3 and t = 7

Time cannot be negative.

So t = 7 sec