# Homework Help: Can I always assume Yi is 0m?

1. Feb 1, 2017

### EinsteinApple

1. The problem statement, all variables and given/known data
A man builds a slingshot that can launch water balloons. If he launches a water balloon at 45.0 degrees to the horizontal at a speed of 35.0 m/s, how far away will the balloon hit?

2. Relevant equations
xf=xi + vix t
vfy=viy+at
yf=yi + 1/2(viy+Vfy)t
yf=yi + viyt + 1/2at^2
vfy2 = viy2a + 2ay

3. The attempt at a solution:

ti = 0
xi=0
yi = 0 (CAN I ASSUME THIS?)
viy = 24.75 m/s
vix = 24.75 m/s
ax=0m/s2
ay=0m/s2

2. Feb 1, 2017

### kuruman

As long as you are consistent with the interpretation of the other given quantities, yes you can.

3. Feb 1, 2017

### EinsteinApple

I just assumed that y2 = 0 because it hits the ground. Therefore, I assumed because he was holding the slingshot y1 couldn't equal 0.
Therefore if y1=0, then y2= a negative value because it's lower.

4. Feb 1, 2017

### kuruman

Is the balloon launched at some height above ground? What is that height?
When you write
yi and yf need to be measured from the same point. That's what what I meant by "consistent".

5. Feb 3, 2017

### CWatters

The problem statement says nothing about the launch or landing height so you have to assume they are the same.