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Old Sep 15th 2009, 11:22 AM   #1
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magnitude of average velocity and derive equation

I'm having difficulties on these questions, I have some ideas on how to solve but not sure if their right.

1. Consider a circular track with a radius of 200 meters, suppose it takes 2 minutes to run from her starting point to the opposite side of the track. What is the magnitude of her average velocity over this 2 minute interval? What is her average speed over the same interval?

I did 400m/120s and got 3.33 m/s, and for speed 400m/120s = 3.33 m/s (should I be putting significant figures also or?

2. Derive Vf^2=Vi^2+2ad (think this is equation for velocity of an object)

I thought that you would treat it like a derivative and comes out to 2Vi+2,
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Old Sep 15th 2009, 10:06 PM   #2
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For the first question, you should also include the direction also and 3 significant figures are alright.

For the second question, you may find the proof easily on the Internet.
Basically are some substitutions, I guess.
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Old Sep 15th 2009, 10:29 PM   #3
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Speed is the distance travelled / time taken i.e. rate of change of distance hence since the runner travels a distance of half the circumference,

$\displaystyle speed\ =\ \frac{1}{2}\ \frac{2\ \pi\ r}{t}$ ,

whereas $\displaystyle vel = displacement /time = \frac {2 \ r }{t} $

as displacement equals the diameter.
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