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Chapter 8 QuickCheck Questions
physics
FOR SCIENTISTS AND ENGINEERS
a strategic approach
THIRD EDITION
randall d. knight
© 2013 Pearson Education, Inc.
QuickCheck 8.2
A toy car moves around a circular track at constant
speed. It suddenly doubles its speed — a change of a
factor of 2. As a result, the centripetal acceleration
changes by a factor of
A. 1/4.
B. 1/2.
C. No change since the radius doesn’t change.
D. 2.
E. 4.
© 2013 Pearson Education, Inc.
Slide 8-38
QuickCheck 8.2
A toy car moves around a circular track at constant
speed. It suddenly doubles its speed—a change of a
factor of 2. As a result, the centripetal acceleration
changes by a factor of
A. 1/4.
B. 1/2.
C. No change since the radius doesn’t change.
D. 2.
E. 4.
© 2013 Pearson Education, Inc.
Slide 8-39
QuickCheck 8.3
An ice hockey puck is tied by a string to
a stake in the ice. The puck is then
swung in a circle. What force or forces
does the puck feel?
A.
B.
C.
D.
E.
A new force: the centripetal force.
A new force: the centrifugal force.
One or more of our familiar forces pushing outward.
One or more of our familiar forces pulling inward.
I have no clue.
© 2013 Pearson Education, Inc.
Slide 8-44
QuickCheck 8.3
An ice hockey puck is tied by a string to
a stake in the ice. The puck is then
swung in a circle. What force or forces
does the puck feel?
A.
B.
C.
D.
E.
A new force: the centripetal force.
A new force: the centrifugal force.
One or more of our familiar forces pushing outward.
One or more of our familiar forces pulling inward.
I have no clue.
The rules about what is or is not a force haven’t changed.
1. Force must be exerted at a point of contact (except for gravity).
2. Force must have an identifiable agent doing the pushing or pulling.
3. The net force must point in the direction of acceleration (Newton’s second law).
© 2013 Pearson Education, Inc.
Slide 8-45
QuickCheck 8.4
An ice hockey puck is tied by a
string to a stake in the ice. The puck
is then swung in a circle. What force
is producing the centripetal
acceleration of the puck?
A.
Gravity
B.
Air resistance
C.
Friction
D.
Normal force
E.
Tension in the string
© 2013 Pearson Education, Inc.
Slide 8-46
QuickCheck 8.4
An ice hockey puck is tied by a
string to a stake in the ice. The puck
is then swung in a circle. What force
is producing the centripetal
acceleration of the puck?
A.
Gravity
B.
Air resistance
C.
Friction
D.
Normal force
E.
Tension in the string
© 2013 Pearson Education, Inc.
Slide 8-47
QuickCheck 8.6
A coin sits on a turntable as the
table steadily rotates ccw. The
free-body diagrams below show the
coin from behind, moving away from
you. Which is the correct diagram?
© 2013 Pearson Education, Inc.
Slide 8-66
QuickCheck 8.6
A coin sits on a turntable as the
table steadily rotates ccw. The
free-body diagrams below show the
coin from behind, moving away from
you. Which is the correct diagram?
© 2013 Pearson Education, Inc.
Slide 8-67
QuickCheck 8.7
A coin sits on a turntable as the
table steadily rotates ccw. What
force or forces act in the plane of
the turntable?
© 2013 Pearson Education, Inc.
Slide 8-68
QuickCheck 8.7
A coin sits on a turntable as the
table steadily rotates ccw. What
force or forces act in the plane of
the turntable?
© 2013 Pearson Education, Inc.
Slide 8-69
QuickCheck 8.8
Two coins are on a turntable that
steadily speeds up, starting from
rest, with a ccw rotation. Which
coin flies off the turntable first?
A.
Coin 1 flies off first.
B.
Coin 2 flies off first.
C.
Both coins fly off at the same time.
D.
We can’t say without knowing their
masses.
© 2013 Pearson Education, Inc.
Slide 8-70
QuickCheck 8.8
Two coins are on a turntable that
steadily speeds up, starting from
rest, with a ccw rotation. Which
coin flies off the turntable first?
A.
Coin 1 flies off first.
B.
Coin 2 flies off first.
C.
Both coins fly off at the same time.
D.
We can’t say without knowing their
masses.
© 2013 Pearson Education, Inc.
Slide 8-71
QuickCheck 8.11
A roller coaster car does a loopthe-loop. Which of the free-body
diagrams shows the forces on
the car at the top of the loop?
Rolling friction can be neglected.
© 2013 Pearson Education, Inc.
Slide 8-82
QuickCheck 8.11
A roller coaster car does a loopthe-loop. Which of the free-body
diagrams shows the forces on
the car at the top of the loop?
Rolling friction can be neglected.
© 2013 Pearson Education, Inc.
The track is above the car, so
the normal force of the track
pushes down.
Slide 8-83
QuickCheck 8.11
A roller coaster car does a loopthe-loop. If the minimum speed
to navigate this loop is 30 m/s,
what is the radius of the track?
© 2013 Pearson Education, Inc.
The track is above the car, so
the normal force of the track
pushes down.
Slide 8-83
QuickCheck 8.11
A roller coaster car does a loopthe-loop. If the minimum speed
to navigate this loop is 30 m/s,
what is the radius of the track?
Fc = F track + Fg (note all are toward the center, positive)
mV2 / r = 0 + mg
V2= rg
(30) 2 = r (10)
r = 90 m
© 2013 Pearson Education, Inc.
The track is above the car, so
the normal force of the track
pushes down.
Slide 8-83
A 1 kg plane moves in a circle (radius of 0.5 m)
at 2 m/s . Find the angle ϴ made between the
cord and the vertical.
© 2013 Pearson Education, Inc.
A 1 kg plane moves in a circle (radius of 0.5 m)
at 2 m/s . Find the angle ϴ made between the
cord and the vertical.
Fc = (1)(2)^2 / (0.5) = 8 N
Fg = mg = (1)(10) = 10 N
Now use trig:
Tan (ϴ) = 8 / 10
So, ϴ = 38.7 o
© 2013 Pearson Education, Inc.
QuickCheck 13.1
The force of Planet Y on Planet X is ___ the magnitude
of X on Y .
A.
B.
C.
D.
E.
One quarter.
One half.
The same as.
Twice.
Four times.
© 2013 Pearson Education, Inc.
Slide 13-29
QuickCheck 13.1
The force of Planet Y on Planet X is ___ the magnitude
of X on Y .
A.
B.
C.
D.
E.
One quarter.
One half.
The same as.
Twice.
Four times.
© 2013 Pearson Education, Inc.
Slide 13-30
QuickCheck 13.2
The gravitational force between two asteroids is 1,000,000 N.
What will the force be if the distance between the asteroids is
doubled?
A.
250,000 N.
B.
500,000 N.
C. 1,000,000 N.
D. 2,000,000 N.
E. 4,000,000 N.
© 2013 Pearson Education, Inc.
Slide 13-31
QuickCheck 13.2
The gravitational force between two asteroids is 1,000,000 N.
What will the force be if the distance between the asteroids is
doubled?
A.
250,000 N.
B.
500,000 N.
C. 1,000,000 N.
D. 2,000,000 N.
E. 4,000,000 N.
© 2013 Pearson Education, Inc.
Slide 13-32
QuickCheck 13.4
Planet X has free-fall acceleration 8 m/s2 at the surface.
Planet Y has twice the mass and twice the radius of
planet X. On Planet Y
A.
B.
C.
D.
E.
g = 2 m/s2.
g = 4 m/s2.
g = 8 m/s2.
g = 16 m/s2.
g = 32 m/s2.
© 2013 Pearson Education, Inc.
Slide 13-37
QuickCheck 13.4
Planet X has free-fall acceleration 8 m/s2 at the surface.
Planet Y has twice the mass and twice the radius of
planet X. On Planet Y
A.
B.
C.
D.
E.
g = 2 m/s2.
g = 4 m/s2.
g = 8 m/s2.
g = 16 m/s2.
g = 32 m/s2.
© 2013 Pearson Education, Inc.
Slide 13-38
QuickCheck 13.6
Which system has more (larger absolute value)
gravitational potential energy?
A. System A.
B. System B.
C. They have the same gravitational potential energy.
© 2013 Pearson Education, Inc.
Slide 13-46
QuickCheck 13.6
Which system has more (larger absolute value)
gravitational potential energy?
A. System A.
B. System B.
C. They have the same gravitational potential energy.
© 2013 Pearson Education, Inc.
Slide 13-47
QuickCheck 13.7
Two satellites have circular orbits with
the same radius. Which has a higher
speed?
A. The one with more mass.
B. The one with less mass.
C. They have the same speed.
© 2013 Pearson Education, Inc.
Slide 13-58
QuickCheck 13.7
Two satellites have circular orbits with
the same radius. Which has a higher
speed?
A. The one with more mass.
B. The one with less mass.
C. They have the same speed.
© 2013 Pearson Education, Inc.
Slide 13-59
QuickCheck 13.8
Two identical satellites have different
circular orbits. Which has a higher
speed?
A. The one in the larger orbit.
B. The one in the smaller orbit.
C. They have the same speed.
© 2013 Pearson Education, Inc.
Slide 13-60
QuickCheck 13.8
Two identical satellites have different
circular orbits. Which has a higher
speed?
A. The one in the larger orbit.
B. The one in the smaller orbit.
C. They have the same speed.
© 2013 Pearson Education, Inc.
Slide 13-61
A really tiny planet named Dinky is orbiting a really tiny
star named Biggerthandinky at a radius of 100 m. If
the velocity of the really tiny planet is 70 m/s, find the
mass of the star in terms of Newton’s Universal
Constant G. Like, 30 G, or 8 G, etc.
© 2013 Pearson Education, Inc.
A really tiny planet named Dinky is orbiting a really tiny
star named Biggerthandinky at a radius of 100 m. If
the velocity of the really tiny planet is 70 m/s, find the
mass of the star in terms of Newton’s Universal
Constant G. Like, 30 G, or 8 G, etc.
Fg=Fc
GMm / r2 = mV2 / r
M = V2 r / G
M = (70)2 (100) / G
M = 490,000 / G
© 2013 Pearson Education, Inc.
QuickCheck 12.1
Two coins rotate on a turntable.
Coin B is twice as far from the
axis as coin A.
A. The angular velocity of A is twice that of B.
B. The angular velocity of A equals that of B.
C. The angular velocity of A is half that of B.
© 2013 Pearson Education, Inc.
Slide 12-28
QuickCheck 12.1
Two coins rotate on a turntable.
Coin B is twice as far from the
axis as coin A.
A. The angular velocity of A is twice that of B.
B. The angular velocity of A equals that of B.
C. The angular velocity of A is half that of B.
© 2013 Pearson Education, Inc.
Slide 12-29
QuickCheck 12.1
Two coins rotate on a turntable.
Coin B is twice as far from the
axis as coin A.
A. The LINEAR velocity of A is twice that of B.
B. The LINEAR velocity of A equals that of B.
C. The LINEAR velocity of A is half that of B.
© 2013 Pearson Education, Inc.
Slide 12-28
QuickCheck 12.1
Two coins rotate on a turntable.
Coin B is twice as far from the
axis as coin A.
A. The LINEAR velocity of A is twice that of B.
B. The LINEAR velocity of A equals that of B.
C. The LINEAR velocity of A is half that of B.
© 2013 Pearson Education, Inc.
Slide 12-29
Where should a student place the fulcrum to
balance this massless 1.6 m beam? The soccer
ball has a mass of 0.8 kg and is located at 0.2 m
from the left. The basketball has a mass of 1.2 kg
and is located 0.2 m from the right .
© 2013 Pearson Education, Inc.
Where should a student place the fulcrum to
balance this massless 1.6 m beam? The soccer
ball has a mass of 0.8 kg and is located at 0.2 m
from the left. The basketball has a mass of 1.2 kg
and is located 0.2 m from the right .
(0.8)(0.2) + (1.2)(1.4)
---------------------------(0.8 + 1.2)
= 1.84 / 2 =
© 2013 Pearson Education, Inc.
0.92 m