11th Grade Physics: Chapter 9
The angle θ in the work equation is the angle between the _____________.
(applied) force and the direction of displacement
List the conservative forces.
-gravitational force -Hooke's Law force (spring force) -electrical force
One common method used to solve dynamic mechanics problems is to use the _____________ of total mechanical energy.
Conservation of Total Mechanical Energy
True/False: 1 J = 1 N/m
False
True/False: A compressed spring will have more kinetic energy than any other kind of energy.
False
True/False: An example of a conservative force is air resistance.
False
True/False: If total mechanical energy is conserved, then we assume that only nonconservative forces are at work.
False
True/False: In a force-displacement diagram for an external force acting on an ideal spring, the area representing the work done by the spring lies above the graph (positive work).
False
True/False: It takes more power to lift 20 books to the shelf in 10 minutes than it would to lift them in 25 seconds.
False
True/False: Lifting a box of 20 books and lifting each of the 20 books the same distance one at a time require the same amount of power.
False
True/False: The rate of doing work is energy.
False
True/False: The same amount of power is needed to do a certain amount of work quickly as to do it slowly.
False
True/False: The spring constant, k, is a dimensionless quantity.
False
True/False: The total mechanical energy of a system is the sum of its kinetic and potential energies, and the work done by nonconservative forces.
False
True/False: The work done by gravity on a falling object is negative because the object's displacement us in the -y direction.
False
True/False: Work is a vector quantity because it is the product of two vectors, force and displacement.
False
True/False: Work is maximum when the angle between the applied force and the system displacement is 90°.
False
Watt
SI unit of power
True/False: 1 W = 1 kg . m^2/s^2
True
True/False: A diving board exerts a Hooke's Law force on the diver.
True
True/False: A falling object may possess both potential and kinetic energy.
True
True/False: It is possible to exert a large force on a system and yet do no work.
True
True/False: Kinetic energy is a scalar quantity even though it involves velocity.
True
True/False: Power is a scalar quantity.
True
True/False: The product of a distance and the component of force that acts over that distance is defined as work.
True
True/False: The reference position for a spring's motion is called its equilibrium position.
True
True/False: When computing the change of the potential energy of a system, you can use any reference position as long as it remains the same for all positions of the system.
True
True/False: Work and energy have the same unit of measure.
True
True/False: Work is a scalar quantity.
True
conservative force
a force that can convert kinetic energy to potential energy and vice versa without loss
ideal spring
a hypothetical object that has no internal resistance, has no mass, and is perfectly elastic
conservation of mechanical energy
a principle that applies to an ideal system that has no energy losses to drag or friction
Hooke's Law
a scientific law that states that within the elastic limit of a material, the restoring force is directly proportional to the displacement of the system from its equilibrium position
spring constant
a value used in Hooke's Law with the units N/m
An ideal spring a. oscillates equal distances on each side of the equilibrium position b. has a small mass c. has a variable spring constant d. has small internal friction e. is made of metal
a.
Peter knocks a book off the 0.9 m-high table and it falls to the floor. Karin picks it up and places it pack on the table. What is the total change in the gravitational potential energy of the book? a. ΔUg = 0 J b. ΔUg = 2 |mg| (0.9 m) c. ΔUg = - |mg| (0.9 m) d. ΔUg = -mv^2
a.
The SI unit of power is the a. watt b. joule c. newton d. kilowatt-hour
a.
The formula Ug = |mg| h is used to determine a. change in gravitational force b. gravitational force c. change in gravitational potential energy d. gravitational potential energy
a.
Which of the following is an example of a nonconservative force? a. air resistance b. gravitational force c. the force a spring exerts on an object d. electric force
a.
For a real-world system, which of the following formulas describes the conservation of mechanical energy? a. K1 + U1 = K2 + U2 b. K1 + U1 = K2 + U2 + Wncf c. ΔK + ΔU = 0 d. ΔK = -ΔU
b.
In theoretical physics, an ideal spring a. exerts the same amount of force throughout its displacement b. has no mass c. has a nearly constant spring constant, k d. does negative work on an attached object
b.
In which case is work zero? a. The force applied in constant. b. Only balanced forces are applied to an object at rest. c. The force applied is parallel to the distance the object is moving. d. Potential energy is changing. e. Kinetic energy is changing.
b.
The force is takes to stretch a spring a. is a constant b. is in the opposite direction to the force exerted by the spring c. is directed toward the equilibrium position of the spring d. varies inversely with the displacement of the spring
b.
Which statement is true about the work-energy theorem? a. It states that the work done on an object is equal to the change in the object's gravitational potential. b. It states that the work done on an object is equal to the change in the object's kinetic energy. c. Work is equal to the sum of an object's kinetic and potential energies. d. The theorem is not valid if the force applied is variable.
b.
A book is lifted up from the floor and put on a shelf with a height, h. Which of the following statements is true, if only conservative forces act on the book? a. ΔK = |mg| h b. ΔK = 1/2 |mv^2| c. ΔU = |mg| h d. ΔU = 0 J e. ΔK = ΔU
c.
In which case is work on a system nonzero? a. The external force applied is perpendicular to the displacement of the system. b. All forces acting on the system are in equilibrium. c. The potential energy of the system increases. d. The potential energy of the system remains constant.
c.
The force exerted by a spring is called a(n) a. oscillating force b. constant force c. Hooke's Law force d. frictional force
c.
Which of the following is an example of a conservative force? a. air resistant b. friction c. the force a spring exerts on an object d. viscous drag
c.
If total mechanical energy is conserved during a process, then we can assume that only ______________ forces are exerted on the system.
conservative
The only types of forces that have potential energy associated with them are ______________.
conservative forces
All of the following contribute to computing power except a. the applied force b. the work done c. the angle between the applied force and the displacement d. the acceleration of the system
d.
All of the following statements about power are true except a. Power is work per unit time. b. P = Fv cos θ c. It takes more power to do work quickly than it takes to do work slowly. d. Power has units of N/s.
d.
How much will the kinetic energy of a school bus increase if its velocity is tripled? a. twice b. thrice c. six times greater d. nine times greater
d.
The slope of a force-distance graph for the force exerted by an ideal spring is equal to a. work b. the acceleration of the spring c. the equilibrium position of the spring d. the spring constant, k
d.
Which of the following is a unit of work? a. slug b. dyne c. newton d. joule
d.
Hooke's Law states that the displacement of a spring is _____________ proportional to the external force acting on the spring.
directly
How much will the kinetic energy of a truck increase if its velocity is increased four times? a. double b. triple c. quadruple d. nine times greater e. sixteen times greater
e.
The tendency of a spring to return to its equilibrium position is because it possessed __________ energy.
elastic potential
A compressed spring possesses _________.
elastic potential energy
The work done by the spring is ____________ the work done on an object attached to the spring.
equal to
The relaxed length for a spring is called its _____________.
equilibrium position
To determine the elastic potential energy of a spring, the displacements of the spring are measured form its ___________.
equilibrium position
The work required to move two objects apart against the force of gravity between them is equal to the change in the _______________ of the objects.
gravitational potential energy
Relative gravitational potential energy depends on gravity, mass, and height measured from the ____________________.
height reference point
The mechanical energy associated with motion is called ______________.
kinetic energy
potential energy
mechanical energy that objects possess because of position or condition
If the angle between the force on a system and its displacement is between 90° and 180°, the work on the system by that force is _____________.
negative
The rate of doing work is __________.
power
For a constant force, what is the shape of the area under the curve of a force-distance graph?
rectangle
Work is a __________quantity.
scalar
The slope of a force-distance graph for a Hooke's Law force is the __________.
spring constant
joule
the SI unit of energy and work
work
the energy transferred to or from a system as a force acts on it through a displacement
energy
the property of a system that gives it the ability to do work
equilibruim
the rest position of a system
total mechanical energy
the sum of the potential and kinetic energy of a system
power
the time-rate at which work is performed
work-energy theorem
the work done on a system by all external forces is equal to the change in the system's kinetic energy
The product of the magnitude of a system's displacement and the component of force that acts on the system parallel to the displacement is defined as _________.
work
In a force-distance graph, the area under the curve best represents _________.
work done
