If a person runs 100 meters at 15 m/s, 400 meters at 10 m/s and 800 meters at 8m/s , what is the average speed?
Speed is given by the relation, speed = distance/ time. This can be written as time = distance/ speed.
Now the person runs 100 m at 15 m/s. The time required is 100/15.
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The time taken by the person to run 100 m at 15 m/s = 100/15 seconds.
The time taken by the person to run 400m at 10 m/s is 400/10 = 40 second.
The time taken by the person to 800m at the speed of 8 m/s = 800/8 = 100 seconds.
So the total distance run by the person = 100+400+800 =1300 meters.
The total time taken by the perso to run 1300 meters = (100/15+ 40+100) s = 146.6667 s.
Therefore the average speed of the person = total distance covered/total time taken = 1300m/146.6667 = 8.86m/s