posted by anonymous .
Two children who are bored while waiting for their flight at the airport decide to race from one end of the 20 -long moving sidewalk to the other and back. Phillippe runs on the sidewalk at 2.0 (relative to the sidewalk). Renee runs on the floor at 2.0 . The sidewalk moves at 1.5 relative to the floor. Both make the turn instantly with no loss of speed.
Who wins the race?
By how much time does the winner win?
t(Phil)= t1+t1 =s/(v+u) + s/(v-u)= 20/(2+1.5)+20/(2-1.5) = 5.7 +40 =45.7 s
t(Phil)- t(Ren=45.7-20=25.7 s