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August 29, 2014

August 29, 2014

Posted by **jane john** on Thursday, June 10, 2010 at 10:48am.

minutes. After running at a constant speed for exactly 27 minutes,

there are still 1100 m to go. The runner then accelerates at

0.2 m/s2 for how many seconds in order to achieve the desired

time?

- physics -
**drwls**, Thursday, June 10, 2010 at 2:27pmThe runner wants to go the remaining 1100 m in 3 minutes. That will require an average speed of 6.11 m/s. His speed for the first 2700 minutes was

8900m/(27*60 s) = 5.49 m/s.

If he accelerates for time T (seconds) and then maintains constant speed for 180-T seconds,

Final speed Vf = 5.49 + 0.2 T

Distance travelled in final 3 minutes

1100 = Vf*(180-T) + (Vf + 5.49)T/2

Substitute 5.49 +0.2T for Vf in the final equation and solve for T.

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