Question

A ball is thrown upward from the balcony of a building and falls to the ground. The height of the ball h meters, above the ground after t seconds is modelled by the function h(t) = -5t^2 + 15t + 45 what is the maximum height?

Answer 1

56.25metres

Explanation:

Given the height of the ball h meters, above the ground after t seconds modeled by the function h(t) = -5t^2 + 15t + 45, at maximum height, the velocity is zero, hence;

dh/dt = 0

Since dh/dt = -10t + 15

-10t+ 15 = 0

-10t = -15

t = 15/10

t = 3/2

t = 1.5secs

Substitute t = 1.5 into the expression given

h(1.5) = -5(1.5)^2 + 15(1.5) + 45

h(1.5) = -5(2.25)+22.5+45

h(1.5) = -11.25+67.5

h(1.5) = 56.25

Hence the maximum height is 56.25metres