# Initial Velocity Question

by MaNiFeST
Tags: initial, velocity
 P: 36 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
 P: 4,777 Are you familiar with conservation of energy?
 P: 36 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
 P: 4,777 Initial Velocity Question Ok, are you familiar with the equations of motion?
 P: 36 I am familiar with the equations for angles ( sin, cos), displacement in X,Y , etc,, for constant/non constant velocities and Trajectories
 P: 4,777 Look through them and try to find one that involves the parameters you think are going to be important and post it.
 P: 36 This isnt really a homework question but w/e Thanks again
 P: 36 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
 P: 4,777 Well, dont solve any equations yet, just look for some that might be useful, and well work from there.
 P: 36 Would this work VFy^2 = VOy^2 + 2a*Displacment Y
 P: 4,777 Aha, you are on to something. Keep going.
 P: 36 Displacment Y = {(Vo^2+sin(2*angle)} / g Only other one i know that doesnt involve time
 P: 4,777 where did this come from? You were on the right track before. Maybe you should take a closer look at your first equation.
 P: 36 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
 P: 4,777 Yes, look at your first equation, and you tell me what each of those terms mean.
 P: 36 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
P: 4,777
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?
 P: 36 VFy That occurs when the object stops right before it comes back down I Know what the terminology means,

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