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 Personal Development for Smart People Forums Just some physics question.

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Join Date: Aug 2007
Posts: 52
Just some physics question.

Hey guys, again, I have a physics HW question that bothers me. I would really appreciate if you could help me with it.

Here's the problem:

Quote:
 A 1,000 kg car traveling with a velocity of +20 meters per second decelerates uniformly at -5.0 m/s/s unitl i comes torest. What is the magnitude of the impulse applied to the car to bring it to the rest?
Now, I know the foruma for impulse is FT but they give you no T.

I would really appreciate you help

 11-06-2007, 09:06 AM #2 (permalink) Senior Member   Join Date: Jun 2007 Posts: 120 If the car is travelling at 20m/s and decelerates at 5m/s/s, how many seconds will it take to come to rest?
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Join Date: Jul 2007
Location: Eugene, Oregon
Posts: 198

Quote:
 Originally Posted by vladtess but they give you no T.
Decelerating at 5m/s^2 from 20 m/s is 4 seconds. So T=4 in this case.

But if I remember from physics class, you don't need time to do it. Impulse = change in momentum. So you can also use mass * change in velocity.

So your change in velocity is -20 m/s
Mass is 1,000 kg

Impulse would be -20,000Ns

or if you use or MV2 - MV1. (Mass*Final - Mass*Initial) you get 1,000*0 - 1,000*20 which is still -20,000

I don't see how you need time in this problem. Then again, I haven't dealt with physics in a few years. Don't listen to me unless you are positive I'm correct, because I have no idea.

 11-07-2007, 09:07 PM #4 (permalink) Family Member   Join Date: Nov 2006 Location: Berlin, Germany Posts: 8,749 It doesn't help you if you let other people do your homework.

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