Educate me please, I have to find initial velocity

[exparrot]

I'm doing a physics lab write-up. It was a projectile lab launching the projectile horizontally. The projectile was launched at a higher elevation (the table) down to the ground.

Homework Statement

Calculate how fast the projectile came out of the launcher. Use the data obtained.

Well, my only data is the distance traveled by the projectile which is 3.7870 m.

Homework Equations

R = √(Rg)/(sin 2θ) ---> since measuring time was not part of the lab, this is the only other equation with no extra unknown variables

The Attempt at a Solution

Don't know how!

How can I solve this given that I only know my distance? I don't know my initial velocity (which I have to find), don't know my final velocity (hesitant to say it's 0 m/s) and my acceleration? I don't think the gravitational acceleration is information integral to this situation since it's horizontally launched. Would supremely appreciate any help, thanks!

 

[sylas]

I'm doing a physics lab write-up. It was a projectile lab launching the projectile horizontally. The projectile was launched at a higher elevation (the table) down to the ground.

[...]

How can I solve this given that I only know my distance? I don't know my initial velocity (which I have to find), don't know my final velocity (hesitant to say it's 0 m/s) and my acceleration? I don't think the gravitational acceleration is information integral to this situation since it's horizontally launched. Would supremely appreciate any help, thanks!

How high was the table? If you didn't measure this, you can't get the result. Just knowing the distance, as you observe, is not going to be enough.

Cheers -- sylas

 

[exparrot]

How high was the table? If you didn't measure this, you can't get the result. Just knowing the distance, as you observe, is not going to be enough.

Cheers -- sylas

0.775 m

 

[drizzle]

what do R and √(Rg) stand for?


ps. the final velocity of a projectile will never be zero, drill that into your mind

 

[exparrot]

what do R and √(Rg) stand for?


ps. the final velocity of a projectile will never be zero, drill that into your mind

R is the range/distance and g is acceleration due to gravity. The original equation was this:

R = [(v0^2)(sin 2θ)]/g

where v0 is the initial velocity. I can't do subscripts here, not sure if I can...

 

[sylas]

0.775 m

That now gives you enough to solve the problem. The next step is part 2: the relevant equations you are using. If you use variables, it will help to say what they represent; as drizzle has also noted.

There may be other equations you should consider...

PS. OK. That's better, but I think you may be using an equation for the range on a flat surface. I've checked; yes, this is not the equation you really want here.

To get subscripts and super scripts, use sub and sup tags.

For example.

input: [noparse]R = (v₀² sin 2θ) / g[/noparse]
result: R = (v₀² sin 2θ) / g

 

[exparrot]

That now gives you enough to solve the problem. The next step is part 2: the relevant equations you are using. If you use variables, it will help to say what they represent; as drizzle has also noted.

There may be other equations you should consider...

I can use the kinematics equations, but my only problem is A) don't know the time as our prof didn't ask us to do that, B) do not know the initial or final velocity. That leaves me with a lot of unknown variables to work with. The speed I calculate in this question is suppose to help me solve subsequent questions.

 

[sylas]

I can use the kinematics equations, but my only problem is A) don't know the time as our prof didn't ask us to do that, B) do not know the initial or final velocity. That leaves me with a lot of unknown variables to work with. The speed I calculate in this question is suppose to help me solve subsequent questions.

Here's a clue. If you launch something horizontally, it takes the same amount of time to reach the ground as if you just dropped it, because the acceleration downwards is still the same, and the initial velocity downwards is 0 in both cases.

 

[drizzle]

edit: ops not for this one :)