# Homework Help: Projectile motion

1. Sep 16, 2007

### innightmare

1. The problem statement, all variables and given/known data

In a local bar, a customer slides an empty beer mug down the counter for a refill. The bartender is momentarily distrated and does not see the mug, which slikde off the counter and strikes the floor 1.40m from the base of the counter. If the height of the counter is 0.860m
a)With what velocity did the mug leave the counter?
b0What was the direction of the mug's velocity just before it hit the floor?

2. Relevant equations
my x-component is 1.40m and y-component is 0.86m
My initial equation would be vyf=vyi + ayt
which turns into (?) 0=visintheta(i)/g

3. The attempt at a solution
I have no idea on how to start computing for this problem. I have no angle for sine, and wouldnt my acceleration be -9.80m/s^2, being that we're dealing with height here????

2. Sep 16, 2007

### learningphysics

What is the equation for vertical displacement?

3. Sep 16, 2007

### innightmare

its deta vector-R=vectorR(f)-vectorR(i)

4. Sep 16, 2007

### learningphysics

Yes, but I was referring to this one:

d = v1*t + (1/2)at^2

can you apply this equation in the vertical direction to this problem?

5. Sep 17, 2007

### innightmare

so what's the value of t? being that time wasnt a given here

6. Sep 17, 2007

### learningphysics

t is what you need to calculate using the equation... getting t will then let you calculate the horizontal velocity.

7. Sep 17, 2007

### Mindscrape

8. Sep 17, 2007

### innightmare

Ooooh ok-got it. For b);
would i find the direction using this equation tantheta=y/x

Thank you so much

9. Sep 17, 2007

### learningphysics

yes, tantheta = vy/vx.