Non-Horizontally launched Projectile

[physics(L)10]

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

 

[rock.freak667]

Well when the ball starts falling back down, what should the vertical velocity be?

 

[physics(L)10]

Yeah, I know that, velocity=0 right? but which equation do I make =0? what do I do after this?

 

[rock.freak667]

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?

 

[physics(L)10]

We don't have a value for Vo though. That's whats confusing me.

 

[rock.freak667]

In that case, I suspect you should find your answers in term of v₀

 

[physics(L)10]

Wtf, how would you do that?

 

[rock.freak667]

Wtf, how would you do that?

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

x=v_xt as x=(v₀cos45)t

Like that.

 

[physics(L)10]

So the only way to do it is to have an unknown variable still there?

 

[rock.freak667]

Yes, you were not given enough information to find v₀

 

[physics(L)10]

So 0= t because anything divided by 0 is 0, correct?

 

[rock.freak667]

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?

 

[Maybe_Memorie]

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..