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July 28, 2014

July 28, 2014

Posted by **jeff** on Wednesday, August 29, 2007 at 4:00pm.

I used the following formula, but was informed my answer was wrong.

100m + (t) 65km/hr = 0 + (t)78km/hr

and solved for (t).

t = 100m / (78km/hr - 65km/hr)

I converted km/hr to m/sec and did the math and got

t = 100m / (21.668 m/sec - 18.057 m/sec)

t = 100m / 3.611 m/sec

t = 27.693 seconds

What did I do Wrong?

- physics- what did i do wrong -
**bobpursley**, Wednesday, August 29, 2007 at 4:25pmThe only thing I see is significant digits. There is no way you can have the answer in five sig digits, given the input data.

- physics- what did i do wrong -
**DrBob222**, Wednesday, August 29, 2007 at 4:40pmIf you leave it in hr, the time for the car to catch the bus is 0.00769 hours.

The bus will travel 0.00769*65 = 0.5 km

The car will travel 0.00769*78 = 0.6 km

The difference is 0.1 km which is the 100 meter separation at th beginning. So the answer MUST be right, at least worked the right way, but the teacher may object to the digits. Perhaps 28 seconds?

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