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I have solved this question several times and the answer turned to be wrong every time.

-A car speeds up uniformly from rest so that it has a velocity of 30m/s after 20s.

How long does it take to travel 250 m?

* putting in mind that the answer is 18 s.

So, I did like this, since it takes 20 s to travel 300 m in the velocity of 30m/s---> so, for travelling 250m it takes the car 16,6 s if we considered the same velocity.

Guest Feb 25, 2017
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A car speeds up uniformly from rest so that it has a velocity of 30m/s after 20s.

How long does it take to travel 250 m?

* putting in mind that the answer is 18 s.

 

\(b=\frac{v}{t}=\frac{30m}{20s^2}=1.5\ m/s^2\)

 

\(s=\frac{b}{2}t^2\)

 

\(t=\sqrt{\frac{2s}{b}}=\sqrt{\frac{2* 250\ m*s^2}{1.5m}}=18.257s\)

 

\(The \ car \ runs \ 18.257\ seconds.\)

 

laugh  !

asinus  Feb 25, 2017
edited by asinus  Feb 25, 2017

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