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An airplane travels at an average speed of 600 m/s on an outward flight and 400 m/s on the return flight over the same distance. What's is the average speed of the whole flight?

Note that the answer is not 500m/s but 480 m/s. Please explain why not?

1 Answer
Dec 4, 2017

let the distance travelled by the the plane during
outward flight#rarr#s

Also distance travelled during return flight#rarr#s

average speed#=##("Total distance")/(Total time)#

Average speed{v}#rArr##(s+s)/((s/v_1)+(s/v_2))#
#V=(2s)/(s((v_1+v_2)/(v_1v_2))#

#color(red)(V=(2v_1v_2)/(v_1+v_2)#

substituting values of #v_1 & v_2#:

#rArr(2xx600xx400)/(600+400)# #=color(green)(480(m)/(s)#