Average Speed = distance/time question.

AI Thread Summary
To calculate the average speed of a race car on a circular track, the formula used is average speed equals total distance divided by travel time. For a track with a radius of 400m, the circumference is calculated as 2πr, resulting in approximately 1256m for one complete lap. When this distance is divided by the lap time of 40 seconds, the average speed is found to be 63m/s. The discussion highlights confusion around the correct formula for circumference and the calculations involved. Ultimately, the correct average speed is confirmed as approximately 63m/s.
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Homework Statement


A race car races on a circular racetrack of radius (r).
(a) Write an equation for the car’s average speed when it travels a complete lap in time (t).
(b) The radius of the track is 400m and the time to make a lap is 40s. Show that the average speed around the track is 63m/s.

Homework Equations


Average Speed = Total Distance/ Travel Time

The Attempt at a Solution


(a) speed = distance/time ?

(b) 400m x 3.14 = 1256m.
63m/s = 1256m/40s.. this is where I get lost. This obviously isn't right. I'm getting an average speed of 31.4m/s.
 
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400m x 3.14 = 1256m is not quite right. What's the formula for circumference again?
 
3. The Attempt at a Solution
(a) speed = distance/time ?

(b) 400m x 2 = 800m = diameter
800m x 3.14 = 2512 = distance
63m/s = 2512m/40s = 62.8m/s
 
Last edited:
negitron said:
400m x 3.14 = 1256m is not quite right. What's the formula for circumference again?

Ty again!

It's been awhile ;(
 
Yes, you have it now.
 
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