# Homework Help: Defenestration homework not going so well -_-

1. Sep 28, 2011

### liagee

A ball is thrown horizontally from the top of
a building 53.8 m high. The ball strikes the
ground at a point 119 m from the base of the
building.
The acceleration of gravity is 9.8 m/s. The time (I got this answer and it's correct and all) is 3.3135sec.
(part 2 of 4) Find the initial velocity of the ball.
(part 3 of 4) Find the x component of its velocity just before it strikes the ground.
007 (part 4 of 4) 10.0 points
Find the y component of its velocity just before it strikes the ground.

vaverage = d/t

a = Vdelta/t

vf = vi + at

I don't even know any others -_-

I tried to use vf^2 = vi^2 + 2ad??????? It didn't work. I am really lost but if someone could tell me which formula (kinematics) to use that would be great.

I already got the time (part 1 of 4) to equal 3.3135sec but despite using the right equations etc I can't get the other three parts.

Last edited: Sep 28, 2011
2. Sep 28, 2011

### Staff: Mentor

The ball was thrown horizontally. How far did it travel horizontally? Over what time? What can change the horizontal velocity?

What's its initial y-velocity? What could change the y-velocity?

3. Sep 28, 2011

### liagee

Accelerationg would change it, and I tried the answer (online homework) in both negative and positive?? The initial y-velocity goes unstated.

4. Sep 28, 2011

### Staff: Mentor

Acceleration would change what in particular?

The ball was thrown horizontally. What does that mean for the x and y components of the initial velocity?

What equation describes the x-position with respect to time? How about the y-position?

5. Sep 28, 2011

### liagee

Acceleration would change the velocity only in the y-direction. Acceleration and therefore velocity in the x-direction remain constant, with accelerationx=0 m/s.

$\Delta$s=vit + .5 (a)(t2)

Thanks so much!!!!!!!

6. Sep 28, 2011

### liagee

Actually that didn't work either -___-

7. Sep 28, 2011

### Staff: Mentor

Didn't work for what? You'll have to be more specific. There are several parts to the problem. What are you trying to find first?

8. Sep 28, 2011

### Staff: Mentor

Sorry if I missed it. What's Defenestration?

9. Sep 28, 2011

### Staff: Mentor

Sorry if I missed it. What's Defenestration?