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Old 06-05-07, 05:12 PM
Physics Help...?
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My wife is getting stuck on something she thinks is probably a simple step. So any help would be appreciated. There is four questions


1) A Boeing 747 "Jumbo Jet" has a length of 59.7m. The runway on which the plane lands intersects another runway. The width of the intersection is 25.0 m. The plane decelerates through the intersection at a rate of 5.70 m/s squared ( I can't type the 2 above the "s") and clears it with a final speed of 45.0 m/s. How much time is needed for the plane to clear the intersection?


2) A cement block accidentally falls from rest from the ledge of a 53.0-m-high building. When the block is 14.0 m above the ground, a man, 2.00 m tall, looks up and notices that the block is directly above him. How much time, at most, does the man have to get out of the way?


3) In 1954 the English runner Roger Bannister broke the four minute barrier for the mile with a time of 3:59.4 s (3 min and 59.4s). In 1999 the Moroccan runner Hicham el-Guerrouj set a record of 3:43.13 s for the mile. If these two runner had run in in the same race, each running the entire race at the average speed that earned him a place in the record books, el-Guerrouj would have won. By how many meters?


4) In 1998, NASA launched Deep Space 1 (DS-1), a spacecraft that successfully flew by the asteroid named 1992 KD (which orbits the sun millions of miles from earth). The propulsion system of the DS-1 worked by ejecting high-speed argon ions out the rear of the engine. The engine slowly increase the velocity of DS-1 by about +9.0 m/s per day. (a) How much time (in days) would it take to increase the velocity of DS-1 by +2700 m/s? (b) What was the eccelration fo DS-1 (in m/s squared)?
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Old 06-05-07, 05:40 PM
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simple, the answer to all 4 is 57.7 meter to the third degree minus the angle at which is acute.
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Old 06-05-07, 06:42 PM
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1. From the moment the jet's nose gets into the intersection to the time its tail clears the intersection, it has moved its length + 25m = 84.7m. So, the question is, how long does it take the plane to go a distance of 84.7m as it is decelerating at 5.7m/s^2 and has a final velocity of 45 m/s.

v^2 = u^2 + 2*a*s

where
v = final velocity = 45m/s
u = initial velocity (unknown)
a = acceleration (-5.7m/s^2)
s = distance traveled = 84.7m

Solve for u, the initial velocity.

Now, use:

v = u + a*t

you just figured out u above and you know v (final velocity) and a (deceleration). Solve for t.
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Old 06-05-07, 06:47 PM
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2. Acceleration due to gravity = a = 9.8 m/s^2

When the man sees the block it is 14 m above the ground. At this point in time, has dropped a distance of 53-14 = 39m and is moving at a speed of v

where v^2 = u^2 + 2*a*s
Since u, the initial velocity = 0, v^2 = 2*a*s. You know a (9.8m/s^2) and s (39m). Solve for v - this will be used as the initial velocity in the 2nd step below.

Now, the block has another 14 - 2 = 12 m to go before it lands on the man's head.

s = u*t + 0.5*a*t^2

where u = initial velocity = what you just found out in the first step. s = 12 m. You know a. Solve the quadratic equation for t.
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Old 06-05-07, 06:53 PM
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3. El-Gerrouj ran the mile in 16.27 sec less than Bannister. So, when El-Gerrouj finishes, Bannister still has 16.27 sec to go to finish. The question is - how many feet does Bannister run in 16.27 sec. You know he runs a mile, i.e. 5280 feet in 239.4 sec, so he runs 22 feet per sec. So,he is 22 x 16.27 = 358.8 feet behind, or 109m behind.

P.S. I assume you really mean a MILE, and not 1600m.
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Old 06-05-07, 06:57 PM
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4. The engine speed increases by 9 m/sec per day which is the acceleration. Since there are 86400 sec in 1 day, the acceleration is 9/86400 = 1.042x10^(-4) m/sec^2.

v = u + a*t where v = final velocity and u = initial velocity, a = acceleration (figured out above) and t = time.

v-u = 2700 m/s
Solve for t.
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Old 06-05-07, 07:55 PM
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Hey Scrumhalf,
This is Shibby's woman.
Thank you so much for working out the problems. It was taking me forever to figure it out simply because I was trying to apply some complicated formulas to it and I was missing the simple steps that were connecting the pieces.
You made my day, thank you again.
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Old 06-05-07, 08:42 PM
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No problem.... it is nice to dust the cobwebs off my brain cells once in a while and solve some physics problems

You only need 3 equations for all of these kinds of problems where acceleration is a constant.

1. v = u + a*t
2. s = u*t + 0.5*a*t^2
3. v^2 = u^2 + 2*a*s

where
u = initial velocity
v = final velocity
a = acceleration
t = time
s = distance traveled

By the way, you might want to double check my math, but the basic method is correct.

Last edited by Scrumhalf; 06-05-07 at 08:47 PM.
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Old 06-06-07, 08:38 AM
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in other words. scrumhalf is doing shibby's wifes homework. i believe this is cheating. i need to contact someone about this. shib, what school does she go to. this is not right!
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Old 06-06-07, 08:39 AM
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p.s. I have no clue what scrumhalf posted above. does that make me a dumbass?
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Old 06-06-07, 09:38 AM
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Quote:
Originally Posted by THE BOUNCER
p.s. I have no clue what scrumhalf posted above. does that make me a dumbass?

There are how many members on this board? And only Scrumhalf answered lol - nice work Scrum! :bravonew:
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Old 06-06-07, 10:22 AM
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Quote:
Originally Posted by THE BOUNCER
p.s. I have no clue what scrumhalf posted above. does that make me a dumbass?
Ask me no questions and I'll tell you no lies... J/K...

I've always been good at physics - I really wanted to be an astronomer growing up but realized in college that my physics chops were not good enough to be a professional physicist, so I settled for engineering instead.

So, this is just some remnants of stuff I learned 25 years ago in high school. I haven't really used any of it since I left college, so don't feel too bad about it.
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Old 06-06-07, 10:56 AM
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Quote:
Originally Posted by Scrumhalf
So, this is just some remnants of stuff I learned 25 years ago in high school. I haven't really used any of it since I left college, so don't feel too bad about it.
Ahaha - don't feel too bad about it.
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Old 06-06-07, 11:39 AM
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Quote:
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There are how many members on this board? And only Scrumhalf answered lol - nice work Scrum! :bravonew:

If I recall correctly, he helped me w/some physics a few years back, lol.
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Old 06-06-07, 04:33 PM
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Originally Posted by THE BOUNCER
in other words. scrumhalf is doing shibby's wifes homework. i believe this is cheating. i need to contact someone about this. shib, what school does she go to. this is not right!
I like to think it's teaching by example I'm so glad that he was able to help, or I know my wife wouldn't have got a good night sleep. She is so dedicated and got real upset a couple years ago when she got her first B. I find it funny, because she married me who was lucky if I passed in high school.
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Old 06-06-07, 05:41 PM
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Quote:
Originally Posted by blm
If I recall correctly, he helped me w/some physics a few years back, lol.
Yeah, I remember that - it was a dimensional analysis question.

http://www.superiormuscle.com/vbulle...ad.php?t=19279

Lots of fun - one tends to get rusty with this kinda stuff after having being out of school for almost 20 years and since I never use this at work.
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Old 06-06-07, 06:28 PM
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because she married me who was lucky if I passed in high school.
me too. i was always pretty smart actually but i just never gave a damn in school.
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Old 06-06-07, 06:36 PM
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You frickin nerd. LOL j/k bro. I wish I was smart.
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Old 06-06-07, 07:38 PM
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Quote:
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simple, the answer to all 4 is 57.7 meter to the third degree minus the angle at which is acute.
:laughnew:
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Old 06-06-07, 08:06 PM
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There are how many members on this board? And only Scrumhalf answered lol - nice work Scrum! :bravonew:
Does it make me smarter than B to know before I ever even opened the thread that Scrumhalf would be the one to help?
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Old 06-07-07, 04:28 AM
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me too. i was always pretty smart actually but i just never gave a damn in school.
I am the same, I just never did my homework. So it all depended on how much homework I got that grading period. Whether my tests (B average there) were a large enough percentage to make me pass.
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Old 06-07-07, 08:25 AM
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I am the same, I just never did my homework. So it all depended on how much homework I got that grading period. Whether my tests (B average there) were a large enough percentage to make me pass.
i pretty much passed 11th and 12th grade because i was friends with the teachers. my high school had an unusual amount of young teachers. all my teachers were in their 20's and early 30's. i flirted with a few of my female teachers. looking back now, i am amazed i never got in trouble for some of the shit i said to them. i used to ask this one teacher that i liked when she was going to leave her husband for me. she would just laugh. LMAO
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Old 06-07-07, 08:30 AM
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i pretty much passed 11th and 12th grade because i was friends with the teachers. my high school had an unusual amount of young teachers. all my teachers were in their 20's and early 30's. i flirted with a few of my female teachers. looking back now, i am amazed i never got in trouble for some of the shit i said to them. i used to ask this one teacher that i liked when she was going to leave her husband for me. she would just laugh. LMAO

These days she would have just banged you while he was at work
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Old 06-07-07, 08:32 AM
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These days she would have just banged you while he was at work
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Old 06-07-07, 08:34 AM
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These days she would have just banged you while he was at work
i was always hoping something like that would happen. never did though. bah..
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Old 06-07-07, 08:39 AM
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i was always hoping something like that would happen. never did though. bah..
You wouldn't want that burden my man - it's a heavy weight to carry especially if you fell for her...

Just keep telling yourself that you could have done her anytime you wanted to but were too much of a man to do such a thing - you'll feel much better about her never giving you the green light ....
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Old 06-07-07, 08:43 AM
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You wouldn't want that burden my man - it's a heavy weight to carry especially if you fell for her...

Just keep telling yourself that you could have done her anytime you wanted to but were too much of a man to do such a thing - you'll feel much better about her never giving you the green light ....
screw that. i would have used that shit to my advantage. i would have asked her for 25% of her salary each month and a blowjob after class each day. otherwise i would tell everyone including her husband.
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Old 06-07-07, 08:44 AM
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screw that. i would have used that shit to my advantage. i would have asked her for 25% of her salary each month and a blowjob after class each day. otherwise i would tell everyone including her husband.
Of course she would counter with the fact she could tell everyone you were hung like a gnat ...
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Old 06-07-07, 08:48 AM
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Of course she would counter with the fact she could tell everyone you were hung like a gnat ...
true. :laughnew:

its a good thing when a girl says, "aww its cute" right?
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Old 06-07-07, 08:49 AM
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true. :laughnew:

its a good thing when a girl says, "aww its cute" right?
Or "it's pretty" or "it's okay" or "I've seen/had worse" or or or ...
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Old 06-07-07, 09:03 AM
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Originally Posted by fog_hat1981
You wouldn't want that burden my man - it's a heavy weight to carry especially if you fell for her...

Just keep telling yourself that you could have done her anytime you wanted to but were too much of a man to do such a thing - you'll feel much better about her never giving you the green light ....

You beat around the bush while everyone else is like "yeah I banged my teacher. How cool am I"....
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Old 06-07-07, 09:23 AM
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You beat around the bush while everyone else is like "yeah I banged my teacher. How cool am I"....
what
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Old 06-07-07, 09:43 AM
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You beat around the bush while everyone else is like "yeah I banged my teacher. How cool am I"....
lol. he would be bitching about how the teacher violated him and how it isnt right and he is now depressed.
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