Physics Help Forum magnitude of average velocity and derive equation

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Sep 15th 2009, 12:22 PM #1 Junior Member   Join Date: Sep 2009 Posts: 6 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,
 Sep 15th 2009, 11:06 PM #2 Senior Member   Join Date: Apr 2008 Location: HK Posts: 886 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. Untitled-5 Basically are some substitutions, I guess. __________________ Good results were achieved and the new task is to become a good doctor.
 Sep 15th 2009, 11:29 PM #3 Physics Team   Join Date: Feb 2009 Posts: 1,425 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.

 Tags average, derive, equation, magnitude, velocity