Quadratic equation word problem

Mar 2010
Hey, I'm having trouble with this one. We've only discussed graphs of quadratic equations that start at (0,0), but this one seems to involve the guy jumping outwards and upwards from above a body of water... does this mean I would start my graph somewhere before (0,0)?

A man jumped upward and outward from a window of a blimp and landed in a body of water. His jump was 120 m, about the height of a 40-storey building. The path of his jump can be represented by the quadratic relationship \(\displaystyle h=120+5.5t-4.9t^2\), where h is the height above the water in metres and t is the time in seconds.

a) Find the maximum height of his dive.

(I thought here you would use the vertex formula... this textbook doesn't have the answer in the back of course...)

b) Find the length of time it took him to reach the water.

Any help would be appreciated!
May 2010
it is all in the equation provided:
if you plot it in the plane (t,h), you find the maximum height as being 121.54 and the h intercept represents the time at which he hits the water at t=5.54s
you could also solve the equation for 120+5.5t-4.9t^2=0 to find the time