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Physics help?

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rvca
Posts: 311 - Karma: 13

During World War I, the Germans had a gun

called Big Bertha that was used to shell Paris.

The shell had an initial speed of 2

an initial inclination of 74

The acceleration of gravity is 9

.32 km/s at.5◦ to the horizontal..8 m/s2 .

How far away did the shell hit? Answer in

units of km.

if anyone can help me ill be VERY happy

How long was it in the air? Answer in units

of s.

Oct 10 2008 5:50PM
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tomahawk
Posts: 2006 - Karma: 53
when i do my physics homework later today or this weekend ill try to help you out with that.

Oct 10 2008 5:53PM
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Rachy
Posts: 4355 - Karma: 2,761
speed of 2 what? km/s? m/s?

inclination of 72 degrees?

I feel like their is info missing... that or im reading it wrong.
Oct 10 2008 5:55PM
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tomahawk
Posts: 2006 - Karma: 53
im pretty sure there is enough info. you gotta make a triangle i think.... and for a parabola.
Oct 10 2008 5:59PM
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rvca
Posts: 311 - Karma: 13

During World War I, the Germans had a gun

called Big Bertha that was used to shell Paris.

The shell had an initial speed of 2

an initial inclination of 74

The acceleration of gravity is 9

.32 km/s at.5◦ to the horizontal..8 m/s2 .

How far away did the shell hit? Answer in

units of km.

Oct 10 2008 6:00PM
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rvca
Posts: 311 - Karma: 13
During World War I, the Germans had a gun
called Big Bertha that was used to shell Paris.
The shell had an initial speed of 2
an initial inclination of 74
The acceleration of gravity is 9
.32 km/s at.5◦ to the horizontal..8 m/s2 .How far away did the shell hit? Answer in
units of km.

sorry this should be all the info
Oct 10 2008 6:02PM
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rvca
Posts: 311 - Karma: 13
lnitial speed of 2.32 km/s at inclie of 74.5 degrees
how far away did it hit? units km
how long was it in the air? seconds
Oct 10 2008 6:05PM
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natedogg789435
Posts: 1177 - Karma: 9
u have an ass faced phisics teacher. my stuff is mad easy
Oct 10 2008 6:07PM
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rvca
Posts: 311 - Karma: 13
ya dude this poop is mad hard. im just not gonna do it
Oct 10 2008 6:10PM
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Edew19
Posts: 365 - Karma: 13
1058.5 km
456.25 seconds
I did that real quick without writing anything down so double check that



Oct 10 2008 6:11PM
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tomahawk
Posts: 2006 - Karma: 53
oh hahah now thats so easy. use the formulas he gave you. i dont remember them that well but ill help you when i have access to my physics book.
Oct 10 2008 6:11PM
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Edew19
Posts: 365 - Karma: 13
oops.. 748.5 km
Oct 10 2008 6:12PM
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Rachy
Posts: 4355 - Karma: 2,761
welp, its projectile motion....

so i know for time spent it is:

time = (2(intial velocity)sin(72))/gravity

and that will give you the time it spends in the air...

so (4sin(72))/9.82 = t

or something to that effect. It looks like he wants to to factor in the earths curvature as well which I don't remember.

As far as the distance traveled, I forgot the physics equation for it, but I know you can do it by creating an equation for the velocity, finding the first derivative to find the speed and then use speed x time = distance.... but thats calculous so there should be an easier way to do it.
Oct 10 2008 6:17PM
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An10a_Eng
Posts: 2505 - Karma: 26

acceleration of gravity is - 9.8

Oct 10 2008 6:22PM
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C-Burg
Posts: 4729 - Karma: 130
break it up into x and y
X:
a(t)=0
v(t)=v0x
x(t)=x0+v0*t

Y:
a(t)=-g
v(t)=v0y-g*t
y(t)=y0+v0y*t-(g*t^2)/2

these are your equations now use your knows to solve for time. Use trig to find v0x and v0y, and x0 and y0 are probably zero(i forgot to look at where it started)
Oct 10 2008 6:23PM
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Inbred_Redneck
Posts: 2776 - Karma: 28
Yeah its projectile motion, we are also doing that unit right now and its kicking my ass.
Oct 10 2008 6:25PM
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Inbred_Redneck
Posts: 2776 - Karma: 28
You have to find t=time first.  Then plug it into the distance equation:
Range= Vx(t) where Vx is your intitial horizontal velocity, or the leg of the triangle if you do it that way.  Range is simply distance.

Hope that helps, its confusing as fuck at first, but i think i'm starting to grasp it now.
Oct 10 2008 6:28PM
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Edew19
Posts: 365 - Karma: 13
i suck, 282.87 km.

fuck it ill write it out.

Vi in the y direction is 2320sin(74.5)=2235.6 m/s (convert km to m)
Vi in the x direction is 2320cos(74.5)= 620 m/s

at the peak of the arch Vf=0 so

Vf=Viy+at
0=2235.6 m/s+(-9.8 m/s^2)(t/2).....t=456.2

for distance:

x=xo+Vixt+1/2gt^2....g=0, xo=0
x= Vix*t= (620 m/s)(456.2 s)=282.87 km






Oct 10 2008 7:08PM
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Jared.
Posts: 1465 - Karma: 59
edew19 is completely correct..i'm in ap physics now and thats exactly what i'd do to figure it out....
i'd say ++ karma to him
Oct 10 2008 7:25PM
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andrew.
Posts: 2349 - Karma: 165
do you want gravitys acceleration to be rounded to 9 or to use 9.8?
Oct 10 2008 11:47PM
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killa_cam
Posts: 13143 - Karma: 15
figure out the time from the vertical component of bullet velocity

t= speed * sin ø / g

distance is speed * t * cos ø

Oct 11 2008 10:29AM
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AKburns
Posts: 464 - Karma: 9
Trick question, the germans didn't know about guns until WW2, they only threw large rocks with their hands and the record distance thrown was 27feet by a man named Valkimuler
Oct 11 2008 10:35AM
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SKIDUBAIGUY
Posts: 3018 - Karma: 8
BOOM goes the dynamite!
Oct 11 2008 10:39AM
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AKburns
Posts: 464 - Karma: 9
alright sorry about the joke response, I did a little research becasue I'm at work and bored, and found that I was right about the trick question part, check it:


The Paris Gun of World War I could hurl a 120 kg shell with 7 kg of explosive to a range of 131 km and an altitude of 40 km.

The Paris Gun of World War I (called by the Germans the Kaiser Wilhelm Gun and often incorrectly termed Lange Max or Big Bertha, two completely different guns)
Oct 11 2008 10:43AM
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mtbakerteacher
Posts: 4185 - Karma: 20
I got 28.36km

Vx= 2.32 sin 74.5 = 2.24 km/s
Vy= 2.32 cos 74.5 = .62 km/s

v=vnot + at
0=.62+ -.098t
-.62 = -.098t
t = 6.33s

But because final velocity was 0 (at the top) multiply by two
12.66s

V=X/T
2.24 = X/12.66
2.24*12.66 = X
X = 28.36km

The teacher wanted the answer in km, not meters.
Oct 11 2008 1:36PM
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mtbakerteacher
Posts: 4185 - Karma: 20
Buuut if they're doing weird things to gravity, then I would get 30.87km if gravity was 9m/s^2
Oct 11 2008 1:38PM
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Edew19
Posts: 365 - Karma: 13
you got your Vx and Vy mixed up.

I only converted to meters out of habit.  Its way too easy to loose track if you don't use SI units although it would have worked here.
Oct 11 2008 2:47PM
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mtbakerteacher
Posts: 4185 - Karma: 20
Word I normally use meters.
and woopsies! SOHCAHTOA
I guess I need trig work
Oct 11 2008 3:27PM
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