Chapter 7 Review

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Chapter 7 Review
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1. In what three ways can an object be
accelerated?
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Speed up, slow down, change direction.
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2. What is the direction of centripetal
acceleration?
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Toward the center of the curve or circle.
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3. A girl swings on a swing set at a linear speed
of 3 m/s. If her center of mass is 2.5 meters
from the point where her swing is attached, what
is her centripetal acceleration?
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aC v2/r aC 32/2.5 aC 3.6 m/s2
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4. A boy goes through the motion of throwing a
baseball. If his arm is one meter long, and the
speed of the ball through the arc of the throw is
15 m/s, what is the centripetal acceleration of
the ball?
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aC v2/r aC 152/1 aC 225 m/s2
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5. What is the direction of centripetal force?
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Toward the center of the curve or circle.
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6. The Spinnaker ride at Six Flags was a spinning
cylinder that pressed its riders against the
inside of the cylinder while the floor dropped
out beneath them. If the cylinder is 10 meters
across and it spins at 28 revolutions per
minute A) What is the centripetal
acceleration? Express this in terms of g.
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28 rev/min x 10p x 1 min/60 s 14.65 m/s aC
v2/r aC 14.652/5 aC 43 m/s2 43 m/s2 / 10
m/s2 4.3 gs
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B) What force is applied to a 70 kg rider?
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F maF 70 x 43 m/s2 F 3010 N
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C) What minimum frictional force must be applied
to the 70 kg rider to keep them from sliding
down the wall?
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Friction must be equal to the weight.Wt mgWt
70 x 10Wt 700 N
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D) If this minimum force is applied, what is the
coefficient of friction between the rider and the
wall?
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m f / FN m 700 / 3010 m 0.233
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7. Two masses are 20 cm apart and have a
gravitational attraction of 20 N. A) If they are
moved to a distance of 40 cm apart, what is the
force between them?
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By F Gm1m2/d2, if d doubles (20 cm to 40 cm),
F must decrease by a factor of 4.20/4 5 N
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B) What is the force if they are moved to a
distance of 10 cm apart?
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By F Gm1m2/d2, if d is halved (20 cm to 10
cm), F must increase by a factor of 4.20 x 4
80 N
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8. Two loaded trucks have masses of 25,000 kg and
27,000 kg. If their centers of gravity are 10
meters apart, what is the force between them?
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F Gm1m2/d2F 6.67 x 10-11 x 25000 x
27000/102F 4.5 x 10-4 N
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9. What is the force of attraction between the
moon and the earth at their maximum separation
distance of 405,000,000 meters? The mass of the
earth is 6 x 1024 kg. The mass of the moon is
7.4 x 1022 kg.
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F Gm1m2/d2F (6.67 x 10-11)( 6 x 1024) (7.4
x 1022)/(4.05 x 108)2F 1.81 x 1020 N
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10. What is the force of attraction between the
moon and the earth at their minimum separation
distance of 363,000,000 meters?
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F Gm1m2/d2F (6.67 x 10-11)( 6 x 1024) (7.4
x 1022)/(3.63 x 108)2F 2.25 x 1020 N
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11. What is the force of attraction between the
earth and Pluto? Plutos mass is 1.3 x 1022 kg
and its average distance from earth is 5.91
billion km.
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F Gm1m2/d2F (6.67 x 10-11)( 6 x 1024) (1.3
x 1022)/(5.91 x 1012)2F 1.49 x 1011 N
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