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December 09, 2019, 06:00:15 pm

Author Topic: velocity  (Read 675 times)  Share 

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fredrick

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velocity
« on: June 10, 2008, 08:19:07 pm »
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A car driven by Jess leaves an intersection and travels due north at 20ms-1 at the same time that a car driven by Kelleaves the intersection due east at 15ms-1.
Calculate the velocity of Kel revative to Jess.

I can get the magnitude of velocity, but the direction?


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Lugo

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Re: velocity
« Reply #1 on: June 10, 2008, 08:30:09 pm »
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I got a relative velocity of 25ms-1 at an angle of 306.87o T

I hope some-one can verify my answer as these relative velocity questions kill me.

cara.mel

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Re: velocity
« Reply #2 on: June 10, 2008, 08:32:36 pm »
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I got - direction: S (arctan(15/20)) E

but it's been ages since I did these
is it just v_(b relative to a) = v_b - v_a
therefore imagine jess is stationary and Kel is moving at 20m/s south and 15m/s east away from her?
bleh. xD

Ken

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Re: velocity
« Reply #3 on: June 10, 2008, 08:49:40 pm »
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i get 217T from tan^-1 [15/20] = 37 and then +180 =217T

fredrick

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Re: velocity
« Reply #4 on: June 10, 2008, 08:53:45 pm »
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i get 143.1T. tan-1(15/20)= 37, then 180-37=143T

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Mao

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Re: velocity
« Reply #5 on: June 10, 2008, 08:54:00 pm »
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how are you guys measuring true bearing?

N xx W?

I thought it was clockwise, i.e. 143 degrees.
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cara.mel

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Re: velocity
« Reply #6 on: June 10, 2008, 09:02:23 pm »
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yeah 143 would be right if you weren't lazy like me :D

Lugo

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Re: velocity
« Reply #7 on: June 10, 2008, 09:35:15 pm »
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Yes I am mistaken,
143oT is correct