Horizontal range of a projectile

[dink87522]

Homework Statement

A ball is tossed from an upper-story window of a building. The ball is given an initial velocity of 7.80 m/s at an angle of 15.0° below the horizontal. It strikes the ground 6.00 s later.
(a) How far horizontally from the base of the building does the ball strike the ground?

Homework Equations

Vx = xsinTheta

DeltaX = Vx . t

The Attempt at a Solution

Vx = 7.8sin(15) = 2.02 m/s^-1

DeltaX = (2.02)(6) = 12.11m

Something is seriously wrong in my answer although I can't see what. The answer should be 45.2m.

 

[dink87522]

I realize I am using Vx = xsinTheta instead of Vx = xcosTheta, although why is it that? When drawing a triangle of this and doing the trig, I get the first equation, could someone please explain this.