Initial Velocity Question

[MaNiFeST]

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

 

[Cyrus]

Are you familiar with conservation of energy?

 

[MaNiFeST]

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, I am not familiar with conservation of energy

 

[Cyrus]

Ok, are you familiar with the equations of motion?

 

[MaNiFeST]

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

 

[Cyrus]

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

 

[MaNiFeST]

This isn't really a homework question but w/e

Thanks again

 

[MaNiFeST]

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

 

[Cyrus]

Well, don't solve any equations yet, just look for some that might be useful, and well work from there.

 

[MaNiFeST]

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

 

[Cyrus]

Aha, you are on to something. Keep going.

 

[MaNiFeST]

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

Only other one i know that doesn't involve time

 

[Cyrus]

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

 

[MaNiFeST]

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 won't have a stop watch when doing this experiment

 

[Cyrus]

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

 

[MaNiFeST]

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

 

[Cyrus]

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?

 

[MaNiFeST]

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

 

[Cyrus]

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?

 

[MaNiFeST]

Thats the thing, I have almost no idea

 

[Cyrus]

Well, you just said it yourself:

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

What does that mean?

 

[MaNiFeST]

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

 

[Cyrus]

Exacttttttly. So what does that mean Vfy =?

 

[MaNiFeST]

VFy = 0 m/s

 

[Cyrus]

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

 

[MaNiFeST]

I can't measure the displacement of Y because it is too great, so I am really stumped

 

[Cyrus]

Why not? Use a really big ruler. Make tick marks on the wall with chalk spaced half a foot apart it comes to that. If the velocity is small, do you think the distance is going to be great?

 

[MaNiFeST]

Ooh i could gently launch it correct? nm , this wouldn't work , the force would be too low than when i launched it a second time

 

[Cyrus]

Sure, why not? You can launch it within reason. In fact, if you have a meter stick, calculate for me right now, what velocity it would need to reach 1 meter?

Let's see if it is resonable.

 

[MaNiFeST]

I wish i could, i would, but all the supplies are at the lab in school :(