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# Physics weird question watch

1. Hey all,

Here is a question that has been really bothering me for quite sometime now:

An Olympic athlete of mass 80kg competes in a 100m race.

What is the best estimate of his mean kinetic energy during the race?

A. 400J B. 4000J C. 40000J D. 400000J

Now if vulgar language was permitted in this forum I would already have used it. LOL.

This question has caused me a lot of pain.

Let us say that the athlete has to push 800N for 100m. Then the work done is 80000J and the average would be half that (40000J)? But that does not make any sense.

Guys, thank you for your help. The help I have received in the Bio and Math forums is priceless. Thank God for such a place as this.

All input appreciated!
2. Since he does 100m in around 10 s his speed is about 10m/s. The average wll be sightly less since he accelerates in the first 2-3 sec then slows down until the finsihing line.

KE = 1/2 m v^2
= 1/2 x 80 x 10^2
3. Ah, how did you get that time of 10 seconds?

Is it ok to make that assumption?
4. Yes - you're expected to know that that is the rough time for an Olympic 100m race!
5. (Original post by batboy)
Ah, how did you get that time of 10 seconds?

Is it ok to make that assumption?
Since this is multiple choice, unless you have this bit of information (which you should have, incidentally, just from living in the world), then the question is really asking you either:

1) to compute the time it would take for someone to run 100m.

Doing this for a few values:
400J ---> 32s
4000J ---> 10s
40000J ----> 3.2s

OR

2) to compute the speed of an athlete over 100m

Doing this for a few values:
400J ---> 3.2 m/s = 7mph
4000J ----> 10m/s = 22mph
40000J ----> 32m/s = 72mph

Then use your judgement with either of these lists of three values. The values for 400J and 40000J in each case are clearly ridiculous for a sprinter, so the most sensible estimate is 4000J.
6. Thanks guys for the input!

I really appreciate that explanation Worzo (now are you really a psychopath?)

I absolutely love the hounds teachercol! I'll do my best to remember that fact of the time of an Olympic race.

I can't tell you guys how long this question has been bothering me. Finally a proper solution.

Also teachercol, I see that you teach IT. I myself am indulging into this new technology call .NET framework (specifically the C# language.)

Thanks again mates for the input!

(Hmm... Worzo, what is the difference between a sociopath and a psychopath? I could never tell the difference.)
7. Slightly off topic, did any athlete actually get 10s in a 100m race - cause that's quite fast!!
8. Okay did some research... Blimey, the fastest is 9.77s: http://en.wikipedia.org/wiki/100_metres
9. (Original post by Eau)
Slightly off topic, did any athlete actually get 10s in a 100m race - cause that's quite fast!!
To be considered a world standard 100m (male) runner you have to be able to run sub 10s to be taken seriously.
10. I could do it in 5.
11. (Original post by batboy)
I could do it in 5.
I can do it in NIIINE-NIIIINE.
12. (Original post by batboy)
I could do it in 5.
minutes
13. Lol

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