Question

An object is thrown upward at a speed of 121 feet per second by a machine from a height of 8 feet off the ground. The height h of the object after t seconds can be found using the equation h = -16t^2+121 t+8
When will the height be 17 feet?




When will the object reach the ground?

Answer 1

17=-16t^2+121t+8
16t^2-121t+9=0
this is a quadratic.
it solves to 7.487seconds and 0.075 seconds.

0=-16t^2+121t+8
16t^2-121t-8=0
this solves to 7.628 and -0.066. obviously the time cant be negative so the only real answer is 7.628 seconds