# Physics

A runner is jogging in a straight line at a steady vr= 2.2 km/hr. When the runner is L= 4 km from the ﬁnish line, a bird begins ﬂying straight from the runner to the ﬁnish line at vb= 6.6 km/hr (3 times as fast as the runner). When the bird reaches the ﬁnishline, it turns around and ﬂies directly back to the runner.
Q1:What cumulative distance does the bird travel? Even though the bird is a dodo, assume that it occupies only one point in space (a “zero” length bird), travels in a straight line, and that it can turn without loss of speed.
Q2: After this ﬁrst encounter, the bird then turns around and ﬂies from the runner back to the ﬁnish line, turns around again and ﬂies back to the runner. The bird repeats the back and forth trips until the runner reaches the ﬁnish line. How far does the bird travel from the beginning (including the distance traveled to the ﬁrst encounter)?I CANT UNDERSTAND please someone explain to me thank you!

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1. let vr = 2.2
The bird flies 4 km to the line: t = 4/(3*2.2) hour
in that time the runner goes 2.2 t = (4/3)km
so the runner is at 4 - 4/3 = 8/3 km from finish when the bird is at finish
now the bird starts back and the runner continues for time T when hey meet
so
(8/3 km) = (runnerspeed*T +bird speed*T
8/3 = T (2.2 + 3*2.2) = 4*2.2 T
T = 2/6.6 Hr = 1/3.3 hr
so how long did the bird fly? t+T
4/6.6 + 2/6.6 = 6/6.6 hours
and how far did it go?
6.6 + 6/6.6*6.6 = 2*6.6 = 13.2km

Part 2 is really easy
it takes the runner 4 / 2.2 hours to finish
the bird flies that whole time so flies
6.6 *4/2.2 = 3*4 = 12 km

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2. whoops, in the first part:
so how long did the bird fly? t+T
4/6.6 + 2/6.6 = 6/6.6 hours
and how far did it go?
(6/6.6)*6.6 = 6 km

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3. What cumulative distance does the bird
A runner is jogging in a straight line at a
steady vr= 8.2 km/hr. When the runner is
L= 4.4 km from the finish line, a bird begins
flying straight from the runner to the finish
line at vb= 49.2 km/hr (6 times as fast as
the runner). When the bird reaches the finishtravel? Even though the bird is a dodo, assume that it occupies only one point in space
(a “zero” length bird), travels in a straight
line, and that it can turn without loss of line, it turns around and flies directly back to
the runner.

speed.

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2. 👎 3

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