Question

A ball is thrown from an initial height of 3 feet with an initial upward velocity of 21 ft/s. The ball height h (in feet) after t seconds is given by the following. h=3+21t-16t^2 find all values of t for which the balls height is 9 feet.

Answer 1

Explanation:

The position equation is given as

`s(t)=-16t^2+21t+3` and we are looking for the times when the position of the ball is 9 feet. That means that we simply plug in a 9 for s(t) and factor to solve for t:

`9=-16t^2+2t+3` and

`0=-16t^2+21t-6` and this is what we factor to find t:

t = .42 sec and then again on its way back down at t = .89 sec