# Initial Velocity Question

Ok So if I were to launch a waterballoon with a waterballoon launcher VERTICALLY , how could I find out the Initial Velocity With OUT a stop watch? My other supplies include a meter stick

Are you familiar with conservation of energy?

This is for a lab at school and you get Extra Credit if you can figure out the first part without a stop watch. Would i have to weigh it? And sorry, im not familiar with conservation of energy

Ok, are you familiar with the equations of motion?

I am familiar with the equations for angles ( sin, cos), displacement in X,Y , etc,, for constant/non constant velocities and Trajectories

Look through them and try to find one that involves the parameters you think are going to be important and post it.

This isnt really a homework question but w/e

Thanks again

Well if I am shooting an object vertically then Displacment X will be 0m, and
Vy = Vo * sin(90) because the degrees will be 90
VFy = 0 m/s

Thats about all the variables i know atm

Im unsure of which equation to use

Last edited:
Well, dont solve any equations yet, just look for some that might be useful, and well work from there.

Would this work
VFy^2 = VOy^2 + 2a*Displacment Y

Aha, you are on to something. Keep going.

Displacment Y = {(Vo^2+sin(2*angle)} / g

Only other one i know that doesnt involve time

Last edited:
where did this come from? You were on the right track before. Maybe you should take a closer look at your first equation.

its equation for X or Y displacment
I am looking for Initial Velocity (Vo) and those two are the only ones that do not include time because i wont have a stop watch when doing this experiment

Yes, look at your first equation, and you tell me what each of those terms mean.

VFy^2 = VOy^2 + 2a*Displacment Y
I am looking for Initial Velocity and not just VOy
Final Velocity of Y = is 0 m/s in this case
VOy^2 = is unknown
a = 9.81m/s^2 in this case
Displacment Y = is also unknown

Ok, we need to get this terminology straight.

$$V_{fy}$$ means the final velocity in the y direction.

$$V_{oy}$$ means the initial velocity in the y direction.

Does this help at all?

Final Velocity of Y = is 0 m/s in this case

Yes, that's correct. Now when does this occur?

VFy That occurs when the object stops right before it comes back down
I Know what the terminology means,

MaNiFeST said:
VFy That occurs when the object stops right before it comes back down
I Know what the terminology means,

How would a ruler be useful given this information? What is the value of Vfy?

Thats the thing, I have almost no idea

Well, you just said it yourself:

VFy That occurs when the object stops right before it comes back down

What does that mean?

It means that in the Y direction, the final velocity is 0 because there is no motion, it suspends in midair

Exacttttttly. So what does that mean Vfy =?

VFy = 0 m/s

Bingo. Now, think about that ruler. What could you do with that ruler now that you have this new information?