hygienistiam Posts: 1, Reputation: 1 New Member #1 Sep 6, 2010, 09:23 PM
Physics question... with answer, yet I don't know how to get the answer.
In order to qualify for the finals in a racing event, a car must achieve an average speed of 270 Km/h on a track with a total length of 1410 m. If a particular car covers the first half of the track at an average speed of 232 km/h, what minimum average speed must it have in the second half of the event in order to qualify? The correct answer is 322.887 km/h.
 ebaines Posts: 12,132, Reputation: 1307 Expert #2 Sep 7, 2010, 06:24 AM

This is a matter of applying the principles that v = d/t and t = v/d. The overall average speed is 1.41 Km/(Total_time), and Total_time is the sum of time for each of the two segments. Note that I convereted the distances to Km for consistency. The time needed for the first segment is 0.705/232, and the time needed for the second segment is 0.705/x, where x is the speed in question. So you have:

$
v_{avg} \ = \ \frac {1.41} {TotalTime} \ = \ \frac {1.41} {\frac {0.705} {232} + \frac {0.705} x}
$

Now solve for x. Hope this helps.
 dshbjDSB11 Posts: 16, Reputation: 1 New Member #3 Jan 6, 2012, 11:50 PM
Werido

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