neeed help with equations (1 Viewer)

[The Spruce Moose]

hey guys i really need help with equations of uniformly accelerated motion stuff like your vertical and horizontal equations the main problem is at times i dunno which to choose and when to find the angle

 

[Minai]

are u talking about projectiles?
you are usually, in most basic questions, given an initial v, and an angle
the horiz v is vcos@ (@ = theta in this case) and vert. velocity is vsin@
to find max height, use s = ut + 1/2at^2
to find time of flight, use v = u + at (v = 0)
to find the range, use s = ut ( i think?)

i dunno, i guess those are just the basics
perhaps the blackjack's or mclake's would wanna elaborate..

 

[The Spruce Moose]

ye dood thats wat i know allready they are the 3 basic equations but what about finding trajectories

 

[BlackJack]

(hmmm....*indecision* you'll see the dilemma if you have read my previous signature... )

Let's use the 'ball just clears the fence example. We're going to find V. We know that it passes through this point x=A y=B, leet's say we also know the angle @
x=Vtcos@
y=Vtsin@ - gt^2

since we know x, we can find t:
t= A/Vcos@
and sub that into equation for y
y= Vsin@ (A/Vcos@) - g(A/Vcos@)^2
And solve.

If we know V and @, and have to find where//if it hits someplace....
You'll be given a height or distance, so you can still work it out with the x and y equations. If you're given y, then it's going to be a quadratic... be prepared)

At Max. h, we've assumed v=0.
This equation... v^2 = u^2 + 2as
u=Vsin@, s is the max height...

If you then want the time, v=u+ at, v-0, and time for full flight is the same w/ v=-u (these velocities verrtical)

Another real example: THe cannon's on top of the cliff, we know it lands in the ocean at x... Given V , @, and x, find height of cliff.
x=Vtcos@; t=x/Vcos@
sub into y.. y'll be negative.

etc., etc. ad infinitum... I probably went too far , but still...

 

[superhubert]

....don't forget the equation

range = (u^2sin2@)/g ....while it isn't in our sylabus it can be mighty handy.....

 

[SkAnDi]

First starting projectiles in 3u... wanted to use physics formulas.

Now back to physics, want to use 3u formulas!

*throws hands up in disgust*

 

[1234567]

i started to do projectiles using 3u ass wel...
bad,,,,,,'

 

[Jellymonsta]

if you want to use that range formula, just derive it
range = horizontal velocity x time of flight
R=vcos@ x (2Vsin@)/g
= (V^2 2sin@cos@) / g
= (V^2sin2@)/g

edit: sorry duffed that. its fixed now.

 

[The Spruce Moose]

oh ok jellymonsta thanx guys for help its just that the fukwit teacher left the topic of science last and we sort of rushed it plus i was absent like from 6 or 7 lessons