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, im 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 isnt 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, dont 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 doesnt 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 wont 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.

[tex]V_{fy}[/tex] means the final velocity in the y direction.

[tex] V_{oy} [/tex] means the initial velocity in the y direction.

Does this help at all?

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