Velocity Word Problem

Question

A ball is thrown upward with an initial velocity of 42 meters per second from a cliff that is 10 meters high. The height of the ball is given by the quadratic equation h=-4.9t^2+ 42t+70 where h is in meters and t is the time in seconds since the ball was thrown. Find the time that the ball will be 60 meters from the ground. Round your answer to the nearest tenth of a second.

Answer 1

-4.9t^2 + 42t + 70 = 60

-4.9t^2 + 42t + 10 = 0

49t^2 - 420t - 100 = 0

 

quadratic formula says:
t = [420 +or- sqrt ( 420*420 + 4*49*100)]/98

 

The negative case results in negative times.

t = 8.8 seconds