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C6L1V@shaw.ca science forum Guru
Joined: 23 May 2005
Posts: 628

Posted: Sun Jul 09, 2006 8:11 pm Post subject:
Re: question with velocity.



mina_world wrote:
Quote:  hello sir~
maybe, my question look like physics.
if a velocity is t (km/h),
then the acceleration is 1(km/h^2) by differentiation.

Be careful. This is a problem about changing units. So you are saying
that a time of 1 hour, the object is moving at 1 km/h = 1000 m/3600
sec = 1000/3600 m/sec. In other words, in 3600 sec the speed reaches
1000/3600 m/sec. Therefore, in x seconds, the speed is
(x/3600)(1000/3600) m/sec, so v = (1000/3600^2) x m/sec, where x is
time in seconds. Thus, the acceleration is a = 1000/3600^2 m/sec^2.
R.G. Vickson
Quote: 
since t (km/h) = (1000*t)/3600 (m/s),
so, the acceleration is 1000/3600 (m/s^2) by differentiation.
but i know the fact that
1 (km/h^2) = 1000/(3600^2) (m/s^2).
um...i can't my errors.
so, i need your advice. 


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mina_world science forum Guru Wannabe
Joined: 20 Jul 2005
Posts: 186

Posted: Sun Jul 09, 2006 4:03 pm Post subject:
Re: question with velocity.



"José Carlos Santos" <jcsantos@fc.up.pt> wrote in message
news:4hcmg7F1qmtngU1@individual.net...
Quote:  mina_world wrote:
maybe, my question look like physics.
It does, but it is a mathematical question.
if a velocity is t (km/h),
then the acceleration is 1(km/h^2) by differentiation.
since t (km/h) = (1000*t)/3600 (m/s),
This is where the problem lies. The letter _t_ on the left is the time
measured in hours. The letter _t_ on the right *should be* the time
measured in *seconds*, rather than in hours. So, you should have:
t (km/h) = (1000*(t/3600))/3600 (m/s)
Now it is correct. After, say 2 hours, what's the speed? The left side
says it is 2 km/h and the right side says it is 2*1000/3600 m/s, which
is correct (that is, they're equal).
so, the acceleration is 1000/3600 (m/s^2) by differentiation.
but i know the fact that
1 (km/h^2) = 1000/(3600^2) (m/s^2).

yes, i see. thank you very much. 

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José Carlos Santos science forum Guru
Joined: 25 Mar 2005
Posts: 1111

Posted: Sun Jul 09, 2006 3:43 pm Post subject:
Re: question with velocity.



mina_world wrote:
Quote:  maybe, my question look like physics.

It does, but it is a mathematical question.
Quote:  if a velocity is t (km/h),
then the acceleration is 1(km/h^2) by differentiation.
since t (km/h) = (1000*t)/3600 (m/s),

This is where the problem lies. The letter _t_ on the left is the time
measured in hours. The letter _t_ on the right *should be* the time
measured in *seconds*, rather than in hours. So, you should have:
t (km/h) = (1000*(t/3600))/3600 (m/s)
Now it is correct. After, say 2 hours, what's the speed? The left side
says it is 2 km/h and the right side says it is 2*1000/3600 m/s, which
is correct (that is, they're equal).
Quote:  so, the acceleration is 1000/3600 (m/s^2) by differentiation.
but i know the fact that
1 (km/h^2) = 1000/(3600^2) (m/s^2).

Best regards,
Jose Carlos Santos 

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mina_world science forum Guru Wannabe
Joined: 20 Jul 2005
Posts: 186

Posted: Sun Jul 09, 2006 3:27 pm Post subject:
question with velocity.



hello sir~
maybe, my question look like physics.
if a velocity is t (km/h),
then the acceleration is 1(km/h^2) by differentiation.
since t (km/h) = (1000*t)/3600 (m/s),
so, the acceleration is 1000/3600 (m/s^2) by differentiation.
but i know the fact that
1 (km/h^2) = 1000/(3600^2) (m/s^2).
um...i can't my errors.
so, i need your advice. 

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