Quadratic Word Problems

Question

7. A ball is thrown upward from a height of 15 ft with an initial upward velocity of 5 ft/s. Use the formula h(t) = -16t2 + vt + s to find how long it will take for the ball to hit the ground.

Answer 1

h(t) = -16t² + vt + s

v is the initial velocity = 5 ft/sec and s is the initial height = 15 ft.

h(t) = -16t² + 5t + 15

When the ball is on the ground, its height is zero:

0 = -16t² + 5t + 15

Solve for t using the Quadratic Formula. You'll get two answers, one positive and one negative. Since we can't go back in time, the positive answer is the correct one. The units of time are seconds.