Question

A ball is thrown at 14.7 m/s from the top of a 88.2 meter tall building. The equation for the balls height s at time t seconds after the ball is thrown; s(t) = –4.9t2 + 14.7t + 88.2. How many seconds does the ball take to hit the ground?

Answer 1

Set the equation equal to 0.


`0 = -4.9t^(2) + 14.7t + 88.2`

Plug the equation into a graph, and look for a zero.

The graph gives you a zero at t = 6.

Prove that you get a zero at t = 6.

-4.9(6)^2 = -176.4
14.7(6) = 88.2
88.2 = 88.2

-176.4 + 88.2 + 88.2 = 0

Answer 2

When it hits the ground the height s = 0 so we have the equation:-

-4.9t^2 + 14.7t + 88.2 = 0

solving this t = 6 , -3 (ignore the negative

Answer time when it reaches the ground = 6 seconds.