A runner is jogging at a steady 8.5 km/hr. When the runner is 3.8 km from the finiish line, a bird begins flying?
from the runner to
the finish line at 42.5 km/hr (5 times as fast
as the runner). When the bird reaches the
finish line, it turns around and flies back to
the runner
How far does the bird travel? Even though
the bird is a dodo, assume that it occupies
only one point in space (a “zero” length bird)
and that it can turn without loss of speed.
Answer in units of km.
Update:its not 19
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Verified answer
the concept is relative velocity of relative motion ...
total time for the man to end the race is 3.8/8.5 hrs = 0.447 hrs
this means that .. the bird travels with 42.5 kmph for 0.447 hrs ..
==>> distance covered = 42.5 x 0.447 = 19 km ...
i guess you will be uncertain of the answer .. but believe me . this is the right answer .. i did a same kind of sum last week !
The Runner is running at a speed of 8.5 km/h
Given this information, 3.8 km from the finish line the runner will take 3.8/8.5 h , or .447 hours.
Multiply the runner's running time by the bird's flight speed to get your answer.
(.447)(42.5) = 19 km.
Or you could just skip these calculations and say that since the runner is 3.8 km from the finish line and the dodo is flying 5 times as fast as the runner, in the time it takes for the runner to cover the 3.8 km the dodo will cover 5 times as much distance, with (3.8)(5)= 19 .