Thread 16831815

How do I know when to use any of these?
△x = Vx,i(cosθ) * △t
Vf,y = Vi (sinθ) - g △t
Vf,y^2 = Vi^2 (sinθ)^2 - 2g △y
△y = Vi (sinθ)△t - 1/2(g) (△t)^2
△t = 2Vi sinθ / g
t = Vi sinθ / g

Sometimes it's wrong to use a certain one to extract the time for example, even when you can extract it in many ways, one way is the correct one. How can I tell the difference?

>>16831815 (OP)
Try each case and learn it for yourself, and it's literally faster and simpler, you'll also remember it better.
It should be obvious if the end result isn't a concrete number but another equation because you don't have all the "dependencies" to solve the eq.
Also think in the physical meaning of the number and signs, otherwise you would be wasting time, do drawings on a paper, not just a malformed scribble, to reason better.

>>16831815 (OP)
You only memorize the important ones that are easy to memorize, then derive the rest. At most it's gonna be 2 equations, 2 unknowns, so it isn't that hard.

At constant acceleration (which is always in these types of problems), the motion is just a hyperbola. If you don't understand -1/2gt^2 + v_0t + x_0 intuitively, you're doing something wrong. For the same but easier situation, at constant velocity (x1-x0)/t = v.

Always, a = dv/dt = (dv/dx) (dx/dt) = dv/dx v, which means that a dx = v dv. So at constant acceleration, a(x1-x0) = (v1)^2/2 - (v0)^2/2.

If you have confusion over sine and cosine, you need to learn about trig and drawing pictures better.

I don't recall memorizing anything else for projectile equations. As long as you can solve 2 equations-2 unknowns, understand the meaning of trig, and can draw pictures, you don't need anything else iirc.

>>16832018
I didn't even memorize the a(x1-x0) thing btw, I just derived it rn by memorizing the dv/dx = dv/dt / dx/dt or dv/dt = dv/dx * dx/dt. They both lead to the same thing. It's not even memorizing the equation, it's just memorizing the trick - all I'm doing is splitting the initial object into two and conserving units.

>>16831815 (OP)
>He thinks they're all different
Kek ngmi. It's literally all from newtons 2nd law and integration.

>>16831815 (OP)
Learn calculus then all of these are basically the same thing and you don't even need any of them

>>16832109
>>16832121
Yeah he just needs to learn the equation of motion of a ballistic projectile and then he will get the general case

>>16832018
That's a parabola btw, not hyperbola

>>16831928
>>16832018
You're right, the thing that made it difficult for me is that I didn't know like for example when to use the time of ascent instead of the total time. I understood that later.
>>16832121
I still don't know a good source to learning that, anon. Any recommendations?

>>16831928
>>16832018
You're right, the thing that made it difficult for me is that I didn't know like for example when to use the time of ascent instead of the total time. I understood that later.
>>16832121
I still don't know a good source to learn calculus, anon. Any recommendations?

>>16832640
Khan Academy unironically
Or you can pick up a calculus textbook

>>16831815 (OP)
I love this shit

Find maximum flying distance: delta y = 0 since the projectile will be on the ground, solve for time (one is t=0, disregard) , plug the other time solution into delta x

Find the highest rise: a) symmetry argument - since its a parabola the highest rise occurs on the second time solution from above - halved -
Plug that halved time solution into delta y

b) velocity in y direction is 0 in the highest rise, solve for t and plug it into delta y