7.2 Extra Practice

Section 7.2 Extra Practice
STUDENT BOOK PAGES 365–370
1. A bird is headed south with an air speed of 4 km>h.
If a gust of wind blowing due east at 10 km>h, what
is the resultant ground velocity of the bird?
2. A fish can swim at a rate of 5 km>h in still water. At
what angle away from perpendicular to the bank of a
river must the fish swim in order to swim directly
across if the river current is 2 km>h?
3. While riding on a train moving 100 km>h, a baby
throws her rattle at a speed of 3 km>h.
a. If she throws the rattle in the opposite direction
that the train is moving in, what is the speed of the
rattle with respect to the ground?
b. If she throws the rattle across the train
(perpendicular to the motion of the train), what is
the speed of the rattle with respect to the ground?
c. If she throws the rattle at a 45° angle to the motion
of the train, what is the speed of the rattle with
respect to the ground?
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4. A boat heads 30° east of south with a water speed of
10 m>s. It then encounters a 4 m>s current coming
from 45° north of east. Determine the resultant
velocity.
5. An airplane is headed west with a constant velocity
of 500 km>h. The plane encounters a wind from the
north at 80 km>h.
a. What is the magnitude of the resultant vector?
b. In 2 hours, how far will the plane travel?
c. In what direction will the plane travel?
6. Sam wants to swim across a river to a point on the
other side of the river directly opposite from him.
The river is moving at 3 km>h.
a. How fast must Sam be able to swim to make it
possible for him to reach the point directly
opposite him on the other side?
b. If Sam can swim 4 km>h, what direction should he
swim in so that he reaches the point directly
opposite from him?
7. An airplane flies with an air speed of 635 km>h. The
pilot wishes to reach a point 417 km directly to the
south, but a 35 km>h wind is blowing from the west.
a. In what direction should the pilot fly in order to
reach the destination?
b. How long will it take to reach the destination?
8. A river is 1.3 km wide and flows at a rate of 3 km>h.
Helen is piloting a boat that has a speed of 10 km>h
in still water. She leaves the shore with the boat
pointed perpendicular to the shore. A dock lies
directly across the river.
a. How far downstream from the dock will the
current push the boat?
b. How long will it take for the boat to cross the
river?
c. Once she reaches the opposite shore (downstream
from the dock), she turns and heads straight for the
dock. How long does it take her to reach the dock
while steering into the current?
d. If Helen had wanted to reach the dock when she
departed the opposite shore, what direction should
she have pointed the boat in?
Section 7.2 Extra Practice
429

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