A ball is thrown vertically upward from the ground. Its distance in feet from the ground in t seconds is s equals negative 16 t squared plus 256 t. After how many seconds will the ball be 1008 feet from the ground?

7 seconds

Step-by-step explanation:

Given the height equation of the motion;

s = -16t^2 + 256t

At s = 1008 ft

The equation becomes;

1008 = -16t^2 + 256t

16t^2 - 256t + 1008 = 0

Solving the quadratic equation for t;

Factorising, we have;

16(t-7)(t-9) = 0

t = 7 or t = 9

When the ball is going up it would reach the given height at time t = 7 seconds.

When it is coming down it would reach the given height at time t = 9 seconds.