Posted by Lena on Friday, April 17, 2009 at 2:12am.
A blue car moving at constant speed of 10m/s passes a polic car that is at rest. The police car accelerates from rest at 4m/s^2 for 3.0 seconds and then maintains a constant speed. The blue car maintains constant speed for the entire 12 seconds. When does the police car pass the blue car?
The police car accelerates at 4m/s^2 for 3 seconds reaching a final speed of 12m/s^2 and traveling a distance of at^2/2 = 4(3^2)/2 = 18m.
At this 3 second point, the blue car has traveled 3(10) = 30m.
From this point on, the police car will close the existing gap of 12m between the cars at a closing speed of 12 - 10 = 2m/s.
Thus, the police car will overtake, and pass the blue car in 12/2 = 6 seconds or 9 seconds after the blue car started.
ME NO MO
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