Non-Horizontally launched Projectile

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Homework Help Overview

The problem involves a projectile motion scenario where a ball is thrown from the ground at an angle of 45 degrees with an initial speed Vo. The questions focus on the timing of the ball's descent, its maximum height, the duration until it hits the ground, and the landing position.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the conditions under which the ball starts to fall, particularly focusing on the vertical velocity at that moment. There is a debate about which equations to use to find time when the vertical velocity is zero, and how to express answers in terms of the unknown initial speed Vo.

Discussion Status

The discussion is ongoing, with participants exploring various equations of motion and questioning how to handle the unknown variable Vo. Some guidance has been offered regarding the use of horizontal and vertical components of motion, but no consensus has been reached on the next steps.

Contextual Notes

Participants note the absence of a specific value for Vo, which complicates their ability to solve the problem directly. This lack of information is a central point of confusion in the discussion.

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Homework Statement


A ball is thrown from the ground (height=0) with an initial speed Vo at an angle of 45 degrees

a)when does ball start falling to earth
b)what is balls max height
c)How long does it take to hit the ground again?
d)where does the ball hit the ground?

Homework Equations


x=Xo + Uxt + (at^2)/2
z=Zo + Uxt + (at^2)/2

r=(0,0,0)
u=Vo(cos45,0,sin45)
a=(0,0,-g)

The Attempt at a Solution



x= Ut
z=cos45t + (sin45t^2)/2

Now I'm stuck lol
 
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Well when the ball starts falling back down, what should the vertical velocity be?
 
Yeah, I know that, velocity=0 right? but which equation do I make =0? what do I do after this?
 
physics(L)10 said:
Yeah, I know that, velocity=0 right? but which equation do I make =0? what do I do after this?

Well you know that v2=v02+2as, v=v0+at as well as the equation you put. So which one will give you time when v=0?
 
We don't have a value for Vo though. That's what's confusing me.
 
In that case, I suspect you should find your answers in term of v0
 
Wtf, how would you do that?
 
physics(L)10 said:
Wtf, how would you do that?

You have vx=v0cos45 and vy=v0sin45. So when considering horizontal motion, you can write

x=vxt as x=(v0cos45)t

Like that.
 
So the only way to do it is to have an unknown variable still there?
 
  • #10
Yes, you were not given enough information to find v0
 
  • #11
So 0= t because anything divided by 0 is 0, correct?
 
  • #12
physics(L)10 said:
So 0= t because anything divided by 0 is 0, correct?


Where did you get that from?

You have three motion equations

s=ut+1/2at2
v2=u2+2as
v=u+at


For the first, part, which one will give you time when the final vertical velocity is zero?
 
  • #13
physics(L)10 said:
So 0= t because anything divided by 0 is 0, correct?

Not quite.
It's undefined. Plug a number divided by 0 into your calculatior. It'll say Math Error or something like that..
 

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