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4. Quiz
Some questions might have more than one correct answer.
1. Which of the following statements are true?
A.
B.
C.
D.
E.
a potential energy is defined for all forces
a potential energy is defined for all conservative forces
a potential energy is defined for all conservative forces that are internalto the system of interest
a potential energy cannot be defined for a system if external frictional forces are present
a potential energy cannot be defined for a system if internal frictional forces are present
2. A potential energy is associated with which of the following forces?
A.
B.
C.
D.
E.
gravitational forces
spring forces
frictional forces
drag forces
forces that depend only on the coordinates of the particles
3. The mechanical energy of a system is conserved if
A.
B.
C.
D.
E.
the net external work is zero
all the internal forces are conservative
all the external forces are conservative
all the internal forces are conservative and the net external work is zero
all forces, both internal and external, are conservative
4. A block is hung from the ceiling by means of a spring, then is pulled downward and released. Air resistance is
negligible. The total potential energy (gravitational and spring) of the block-spring-Earth system is greatest
A.
B.
C.
D.
E.
only when the block is at the highest point
only when the block is at the lowest point
when the block is either at the highest or lowest point
when the block is at its equilibrium point
when the block is at some other point
5. As a block slides down an incline the incline exerts a frictional force on it. For which system is energy conserved?
A.
B.
C.
D.
E.
the system consisting of
the system consisting of
the system consisting of
the system consisting of
the system consisting of
the block and incline
the block and Earth
the incline and Earth
the block alone
the block, incline, and earth
6. A block is hung from the ceiling by means of a spring, then is pulled downward and released. It oscillates, subject
to air resistance. For which system is energy conserved?
A.
B.
C.
D.
E.
the system consisting of
the system consisting of
the system consisting of
the system consisting of
the system consisting of
the block alone
the block and spring
the block, the spring, and Earth
the block, spring, Earth, and the air
the block, Earth, and the air
7. A pendulum hangs from the ceiling and swings back and forth. Which of the following statements is true if air
7. A pendulum hangs from the ceiling and swings back and forth. Which of the following statements is true if air
resistance can be neglected?
A. the Earth-pendulum system has its greatest potential energy when it is at its highest point
B. the Earth-pendulum system has its greatest kinetic energy when it is at its highest point
C. the Earth-pendulum system has its greatest potential energy when it is at its lowest point
D. the Earth-pendulum system has its greatest kinetic energy when it is at its lowest point
E. both the kinetic and potential energies of the Earth-pendulum system remain constant throughout the swing
8. A system consists of several objects. It starts with certain values of its kinetic and potential energies. Sometime later
it returns to its starting configuration but with less kinetic energy. If no external forces act on the objects of the
system, we must conclude that
A.
B.
C.
D.
E.
the objects exert nonconservative forces on each other and the thermal energy of the system has increased
the objects exert nonconservative forces on each other and the thermal energy of the system has decreased
the objects exert nonconservative forces on each other and the thermal energy of the system has not changed
the objects exert conservative forces on each other and the thermal energy of the system has increased
the objects exert conservative forces on each other and the thermal energy of the system has decreased
9. A crate slides across a level floor. The frictional force of the floor on the crate
A.
B.
C.
D.
E.
increases both the kinetic and thermal energies of the crate
increases the kinetic energy of the crate and decreases its thermal energy
decreases the kinetic energy of the crate and increases its thermal energy
decreases both the kinetic and thermal energies of the crate
does not change the thermal energy of the crate
Answers: Answers: (1) C; (2) A, B; (3) D; (4) A; (5) E; (6) D; (7) A, D; (8) A; (9) C
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