muff528 3
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kallend 1,673
QuoteWell, I would have a different opinion depending on whether this is a physics or math instructor. Physics is supposed to model reality to some extent.
well I agree with that although, it seems like this is a 100 level trig based physics class so making unrealistic assumptions is sometimes needed to prove points.
I don't believe unrealistic assumptions PROVE anything except to be skeptical about assumptions.
I lead my 200 level class through an entire class long derivation of the strength of a crystal, only to tell them at the end of all the math that the answer is actually wrong by a factor of 1,000 because the initial assumption, which they all believed without question, was incorrect.
...
The only sure way to survive a canopy collision is not to have one.
The only sure way to survive a canopy collision is not to have one.
Here are Usain Bolt's splits from the 2008 Olympics in Beijing when he ran the 100m in 9.69. If your professor is claiming that is a real performance in the Olympics then this is the only one it could be:
Reaction time: .165
0-10 meters: 1.85 (this split includes reaction time)
10-20 meters: 1.02
20-30 meters: .91
30-40 .87
40-50 .85
50-60 .82
60-70 .82
70-80 .82
80-90 .83
90-100 .90 (celebrated early)
So yes, you are correct, he reached top speed by about 50 meters in and maintained it just about the whole way to the end. His top speed was just over 27 mph.
Edited to add: I'm not a math nerd but I am a huge track and field nerd.
Reaction time: .165
0-10 meters: 1.85 (this split includes reaction time)
10-20 meters: 1.02
20-30 meters: .91
30-40 .87
40-50 .85
50-60 .82
60-70 .82
70-80 .82
80-90 .83
90-100 .90 (celebrated early)
So yes, you are correct, he reached top speed by about 50 meters in and maintained it just about the whole way to the end. His top speed was just over 27 mph.
Edited to add: I'm not a math nerd but I am a huge track and field nerd.
"What if there were no hypothetical questions?"
MBiegs 0
I was saying that A would be constant in the 1st half and 0 in the 2nd half.
It's actually a basic class on car accidents. My instructor was using formulas we learned in class to show how they can be used in other situations.
Most of our formulas/drag factors/calculations are geared to give the drivers the benefit of the doubt and we're usually not figuring ending velocity, but beginning velocity.
FYI: I got the 175 feet from the 50-60 mark that's listed at http://en.wikipedia.org/wiki/100_metres
Although it says he maxes speed 50-60, i'm sure he could come close to max way before that. A olympic athlete should be able to max way before the average person... thus lowering the ending velocity.
I just wanted to prove to a classmate that the answer of 45mph doesn't make sense... and show him that i could make it lower by breaking it into two parts... i'm sure it'd be lower in 3 or 4 parts, but that's overkill for what i'm trying to show.
In the end my instructor/classmate probably wont care, and i probably won't even bring it up... but it's giving me something to do while putting off everything else I should be doing.
Thanks everyone
It's actually a basic class on car accidents. My instructor was using formulas we learned in class to show how they can be used in other situations.
Most of our formulas/drag factors/calculations are geared to give the drivers the benefit of the doubt and we're usually not figuring ending velocity, but beginning velocity.
FYI: I got the 175 feet from the 50-60 mark that's listed at http://en.wikipedia.org/wiki/100_metres
Although it says he maxes speed 50-60, i'm sure he could come close to max way before that. A olympic athlete should be able to max way before the average person... thus lowering the ending velocity.
I just wanted to prove to a classmate that the answer of 45mph doesn't make sense... and show him that i could make it lower by breaking it into two parts... i'm sure it'd be lower in 3 or 4 parts, but that's overkill for what i'm trying to show.
In the end my instructor/classmate probably wont care, and i probably won't even bring it up... but it's giving me something to do while putting off everything else I should be doing.
Thanks everyone
MBiegs 0
That's it.
Track and field nerd, that's a new one. 
QuoteThat's it.
Track and field nerd, that's a new one.
Bolt is actually outstanding in is speed endurance. Most sprinters are slowing down by 70m. Bolt reached a higher top speed and then held onto it better than any sprinter ever.
"What if there were no hypothetical questions?"
QuoteQuote
Is this a cheetah?
Unladen swallow.
African or European?
(.)Y(.)
Chivalry is not dead; it only sleeps for want of work to do. - Jerome K Jerome
Niki1 1
QuoteQuote
Is this a cheetah?
Unladen swallow.
Is it an African Swallow or a European Swallow?
Most of the things worth doing in the world had been declared impossilbe before they were done.
Louis D Brandeis
Where are we going and why are we in this basket?
Louis D Brandeis
Where are we going and why are we in this basket?
pyrotech 0
QuoteA man runs 325 feet in 9.7 seconds. Assuming a continuous rate of acceleration he would be running at 45mph by the end of the run... seems wrong because in reality his acceleration isn't constant. Through research I have learned a sprinter would reach max speed approximately half way through(distance). This is where I need your help...
Assuming he still runs 325 feet in 9.7 seconds, also assume he reaches his maximum speed at the 175 foot mark and his speed is constant for the remainder of the run:
What speed is he at the 175 foot mark?
How long did it take him to get to the 175 foot mark?
Would you prefer an equation for your answer or are we allowed to make assumptions of either his top speed or time it took to get to 175 ft? Can't have both.
Your professor was correct (though I got a little less than 47mph, and an average of 22.8mph... I think I missed a step somewhere in calculating max speed), because he said to 'assume.' If you're wanting a definite answer to a variable environment, you have to make assumptions. The man could have reached 80mph at one point and slowed down if the assumption was not made. There were times when I was writing out a proof to a theorem and thought "why would we assume that? This is more probable," but have to realize that in math, when variables change, we have to assume.
EDIT: If we assume the max speed of the runner was 50mph, the runner would reack 175ft in 7.555 seconds
I would think the runner would hit top end waaayy before the 175 ft. mark (really in just a few feet), reducing the top end speed but maintaining it for longer. The 9.7 in itself is not unrealistic for a 325 ft. sprint.
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