The function is the height of a foot ball at sec  after kickoff.

Horizontal line test:

A function is one-to-one if and only if no horizontal line intersects its graph more than once.

That is, any horizontal line in the graph must cross the curve at one point only.

The path of the ball is parabola during the ball is in the air.

Graph: 

Graph the rough sketch of the trajectory of the football.

Draw the horizontal line .

Observe the graph:

The horizontal line touches the graph twice.

.

The function is not an one-to-one, because it violates the horizontal line test.

The function is not an one-to-one function.