Homework Help: physics

Posted by priya on Tuesday, June 15, 2010 at 4:18am.

On a 120km track,a train travels the first 30km at a uniform speed of 30km/hr.how fast must the train travel the next 90km so as to average 60km/hr for the entire trip?

physics - MathMate, Tuesday, June 15, 2010 at 7:50am
The train travelled 30km at 30km/hr. It took therefore 30/30=1 hr.
To attain an average of 60km per hour over 120 km, the total time must be 120/60=2 hours.
There is (2-1)=1 hour left to do the remaining 90km. What should be the speed?

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