Pointless physics question

kennisondan · Post by **kennisondan** » Wed Jan 21, 2009 8:43 pm

Well being an attorney instead of an engineer; my answer is :

WHAT WOULD YOU LIKE THE OUTCOME TO BE ?
WE CAN CALL IT THAT..
DK

UrbanSherpa · Post by **UrbanSherpa** » Wed Jan 21, 2009 8:48 pm

ComfyBear wrote:How ungrateful !

The reason I don't is because unless you know and you can state all the variables that exist, there is NO definitive answer.

Furthermore, if the truth be know, to quote you, it's a pointless question; hardly worthy of an answer.

So if it's a question you must answer for your physics class....you're on your own.

ComfyBear,
My intent was certainly not inflammatory. Please don't receive it as such.
Judging by the interest (views/replies) it is worthy. Also, young man, the last physics class I took was in the 70's (shortly after your cut/paste rocket formulae put Neil on the moon)

I digress. Just trying to answer a Q for a co-worker. I'm still open to qualified answers, though.

Pydpiper · Post by **Pydpiper** » Wed Jan 21, 2009 8:56 pm

You can't start a thread with the word "pointless" and expect quantified or qualified answers.
But, I love the concept. I will supply the bow, arrows, clear evening, large field, tracer nocks and helmets, you supply the means to measure the out come and we can get to the the bottom of this!

Boo · Post by **Boo** » Wed Jan 21, 2009 8:58 pm

UrbanSherpa wrote:
ComfyBear wrote:How ungrateful !

The reason I don't is because unless you know and you can state all the variables that exist, there is NO definitive answer.

Furthermore, if the truth be know, to quote you, it's a pointless question; hardly worthy of an answer.

So if it's a question you must answer for your physics class....you're on your own.
ComfyBear,
My intent was certainly not inflammatory. Please don't receive it as such.
Judging by the interest (views/replies) it is worthy. Also, young man, the last physics class I took was in the 70's (shortly after your cut/paste rocket formulae put Neil on the moon)

I digress. Just trying to answer a Q for a co-worker. I'm still open to qualified answers, though.

Hehehe, it doesn't take much to catch our interest! LOL!

ComfyBear · Post by **ComfyBear** » Thu Jan 22, 2009 9:21 pm

Judging by the interest (views/replies) it is worthy. Also, young man, the last physics class I took was in the 70's (shortly after your cut/paste rocket formulae put Neil on the moon)

For starters, I didn't take your reply as inflammatory, after all, as a fireman, I would think your job is to put out fires, not start them. So no offence taken

As far as the worthyness of your question, I was just quoting your statement.

As for being a young man, I'm probably as "young" as you, since I too took Grade 13 physics in 1970.

"Just one small step for man, one giant leap for mankind."

As far as my cut and paste formula, someone with a PhD in Physics wouldn't need to resort to that, however it does save a lot of typing.

In all seriousness, there is not a definitive answer to your question, because of the unknown variables.

However, if you're really interested in knowning what's in involved, I'll supply further information, using a bullet fired from a gun.

Not only will I give you the formula for how high it will go, but also give you additional formulae for the time it would take to go up and come down, and it's speed at any given time. That's as much of my time I'm willing to devote to your question. If it doesn't suffice, so be it.

Once again, neglecting friction and assuming that you fire it directly up in the air, it's a dead simple question.

u=initial velocity
v=final velocity
a=acceleration
s=displacement (distance from origin, ie height)
t=time

v^2=u^2+2as (I could derive this but can't be bothered to figure it out)
now the intial velocity is the muzzle velocity, the final velocity is zero (we're interested in when the bullet stops and starts to fall back down), the acceleration is -9.8. I'm choosing upwards to be the positive direction, therefore gravity is negative.

0=u^2 - 20*s
s=u^2/20

So the height is the muzzle veoloctiy squared, divided by 20.

The time it took would be:
from v=u+at
t=u/10
the muzzel velocity / 10
The time to hit the ground is twice that, by symmetry.

You can calculate the velocity of the bullet at any time using this equation
v=u+at
or any height using s=ut+(1/2)*a*t^2.

You have to make sure that you stick to your sign convention that velocities upwards are positive and those downwards are negative.

If the bullet wasn't going straight up, you treat the horizontal and vertical components of it's velocity seperately.

The vertical component would be
u_v=u*cos(a) where a is the angle from straight up.

The horizontal would be
u_h=u*sin(a)

The horizontal velocity is constant so once youve subbed the result for u_v into the equation for time to hit the groud, you can calculate how far the bullet travelled horizontally just by using velocity=distance/time.

UrbanSherpa · Post by **UrbanSherpa** » Thu Jan 22, 2009 10:45 pm

ComfyBear,

I do like the 'bullsh*t baffles brains' formulae, although I still can't find any resemblance to a final answer.

I didn't intend for this "pointless" thread to devolve into a pissing match so let's call it quits, it is getting rather childish, especially for a 56 yr old.

........unless you feel the need to get the last reply in.

ComfyBear · Post by **ComfyBear** » Thu Jan 22, 2009 11:45 pm

Bueller
If it's a truce you want, your wish is my command, especially since I never for one moment viewed our discourse as a "pi$$ing match", but rather fun while it lasted.
In parting, may I suggest that in the future, if you wish to be taken seriously, refrain from stating that your question is pointless, otherwise you ask your questions, you take your chances.

Peace Bro', may the force be with you

K-Man · Post by **K-Man** » Sun Jan 25, 2009 10:44 am

Hey Pyed,

That must have been before you took the Hunter Safety Course. No Cordoba's in the regs these days.

K-Man

wabi · Post by **wabi** » Sun Jan 25, 2009 4:47 pm

How high would an arrow (bolt) go if fired straight up in the air from a crossbow?

Posted the answer on the wrong thread, but I have it for a compound bow!
Now to get the answer on the right thread

From a 55# compound bow shot straight up on a day with no wind from a location 985' above sea level with a barometric pressure of 30.3 and a temperature of 28.4F it went 406 yards according to my rangefinder!

Grizzly Adam · Post by **Grizzly Adam** » Sun Jan 25, 2009 4:55 pm

wabi wrote:

LOL

UrbanSherpa · Post by **UrbanSherpa** » Mon Jan 26, 2009 8:58 am

Grizz,

That is great!!!! You made me laugh.

I wonder what went thru your mind when the answer hit you

Now get to a doctor.....fast!!!!

Boo · Post by **Boo** » Mon Jan 26, 2009 9:42 am

UrbanSherpa wrote:Grizz,

That is great!!!! You made me laugh.

I wonder what went thru your mind when the answer hit you

Now get to a doctor.....fast!!!!

LOL!!!

Hey Mike, does it hurt?

Grizzly Adam · Post by **Grizzly Adam** » Mon Jan 26, 2009 10:14 am

UrbanSherpa wrote:Grizz, That is great!!!! You made me laugh. I wonder what went thru your mind when the answer hit you Now get to a doctor.....fast!!!!

Hey, 'Sherpa ... it's Wabi's pic! I was just laughing at it. Still am!