True or false: An engine does work on a car when the car is moving uses work in the scientific sense.
True
True or False: Joseph found that holding the banner in place was hard work uses work in the scientific sense.
False
True or False: Anne did work on the project for 5 hours uses work in the scientific sense.
False
True or False: Stan goes to work on the bus uses work in the scientific sense.
False
Work is done on an object whenever a force causes what?
Displacement of the object.
True or false: Work is done when a weightlifter lifts a barbell.
True
True or False: Work is done when a weightlifter holds a barbell overhead.
False
True or False: Work is done when a weightlifter slowly lowers a barbell.
Ture
True or False: Work is done when a weightlifter drops a barbell and the barbell falls to the ground.
True
If the sign of work is negative then what?
The component of the force that does wok is in the direction opposite the displacement.
A painter lifts a bucket of paint carries it 5 m horizontally, then sets it back down. What is true about the force of gravity when the worker lifts the bucket?
The force of gravity does negative work when the worker lifts the bucket.
What is the equation used to calculate the work done on an object by a force at an angle, 0, to the displacement?
W=Fdcos0
A joule is equivalent to what?
N X m
A parachutist falls at a constant speed for 200m. What is the only force doing work on the parachutist?
Air resistance
A construction worker lifts a heavy cinder block 1m off the ground, holds it in place for 3s, then sets it back down in the same place. Describe the forces doing work on the block and the net work on the block throughout this action.
When you lift and put things down, the force acting on it is gravity and natural force. These make up the net force.
What is kinetic energy?
Energy that is due to the motion of an object.
What is gravitational potential energy?
Energy stored in the gravitational field of interacting bodies.
What is elastic potential energy?
Energy associated with a compressed or stretched object.
How does the kinetic energy of an object change if the object's speed doubles?
The kinetic energy increases by a factor of 4.
What does the work-kinetic energy theorem state?
The net wok done on an object equals the change in the kinetic energy of the object.
Friction does-400J of net work on a moving car. How does this affect the kinetic energy of the car?
the kinetic energy decreases by 400 J.
What does not affect gravitational potential energy?
An object's speed.
How does the elastic potential energy in a mass-spring system change if the displacement of the mass is doubled?
The elastic potential energy increases or decreases by a factor of 4.
What is true of the conservation of energy in a closed system?
Total energy is always conserved.
True or False: Total energy is always conserved in a closed system?
True
The mechanical energy of a system of objects is the sum of kinetic energy and all relevant forms of what kind of energy?
Potential
When is mechanical energy not conserved?
When friction is not negligible.
True or False: Mechanical energy most likely to be conserved when a football flies through the air.
True
True or False: Mechanical energy most likely to be conserved when a feather falls from the sky.
False
True or False: Mechanical energy most likely to be conserved when a skateboard rolls into the grass.
False
True or False: Mechanical energy most likely to be conserved when a skateboard rolls into the grass.
False
True or False: Mechanical energy most likely to be conserved when a hockey player digs his skates into the ice.
False
If mechanical energy is conserved in a system, the energy at any point in time can be in the form of what?
kinetic energy, gravitational potential energy, and elastic potential energy.
What is evidence that frictional forces are present in a system?
Interactions in the system cause in increase in temperature, it produces sound, and mechanical energy is not conserved.
An egg suspended above the ground has 2.0 J of gravitational potential energy. The egg is then dropped and falls to the ground. What is the kinetic energy of the egg just as it reaches the ground?
2.0 J
The SI unit for power is what?
W
If a machine increases the distance over which work is done, the force required to do the work is less, more, are the same?
Less
If a machine decreases the distance over which work is done, the force the machine applies is greater, less, or the same?
Greater
A 100 W light bulb converts 100 J of what kind of energy to other forms of energy each second?
Electrical energy
Work is defined as what?
W=Fd
W=Force(Newtons)X displacement(m)
What is work?
The product of the component of a force along the direction of displacement and the magnitude of the displacement.
When the force on an object and the object's displacement are in different directions. only the component of the force that is parallel to the object's displacement does work. True or False?
True
What is the equation for new work done by a constant net force?
Wnet=FnetCos0
Net work=net force X displacement X cosine of the anlge between them
How is joules represented?
(N X m)
newtons times meters
True or false: work is a scalar quantity and can be positive or negative
True
If the net work is positive, the object's speed what?
Increases
If the net work is negative, the object's speed what?
Slows down
True or false: kinetic energy is energy associated with an object in motion
True
When a force is constant, so is the what?
Acceleration
Kinetic energy depends on what?
Speed and mass
The energy of an object that is due to the object's motion is what kind of energy?
Kinetic
What is the equation for kinetic energy?
KE=1/2mv2
What kind of quantity is kinetic energy?
Scalar
If traveling at the same speeds, which one has more kinetic energy? A volley ball or a bowling ball?
A bowling ball
True or False: The net wok done on a body equals its change in kinetic energy?
True
What is the work-kinectic energy theorem?
Net work= change in kinetic energy
What does the work-kinectic energy theorem state?
That the net work done by all the forces acting on an object is equal to the change in the object's kinetic energy.
True or False: Potential energy is not stored energy
False. Potential energy is stored energy
What is the definition of potential energy?
The energy associated with an object because of the position, shape, or condition of the object
What equation can you use to solve for gravitational potential energy?
Gravitational potential energy=mass X free-fall acceleration X height
What is the definition of gravitational potential energy?
It is the potential energy stored in the gravitational fields of interacting bodies
What does gravitational potential energy depend on
Height and the free-fall acceleration
What does elastic potential energy depend on?(compressed or stretched)
Distance
Elastic potential energy is stored in any compressed or stretched object. True or false
True
What is the definition of elastic potential energy?
The energy available for use when a deformed elastic object returns to its original configuration.
What is the formula for elastic potential energy?
Elastic potential energy=1/2 X spring constant X (distance compressed or stretched)2
Spring constant is also known as what?
Force constant
What is the definition of spring constant?
A parameter that is a measure of a spring's resistance to being compressed or stretched.
What does it mean when something is conserved?
It remains constant
True or false: Mass is conserved
True
Define mechanical energy.
The sum of kinetic energy and all forms of potential energy
What is classified as non mechanical energy?
Nuclear, chemical, internal, and electrical energy.
Adding the kinetic and potential energy gives the total what?
Mechanical energy at each position
True or false: In the absence of friction, the total mechanical energy changes.
False.In the absence of friction, the total mechanical energy remains the same.
What is the equation for conservation of mechanical energy?
initial mechanical energy= final mechanical energy (in the absence of friction)
When does energy conservation occur?
When acceleration varies
When is mechanical energy not conserved?
In the presence of friction
True or false: Total energy is never conserved
False. It is ALWAYS conserved
The rate at which work is done is called what?
Power
What is power?
A quantity that measures the rate at which work is done or energy is transformed.
More generally, power is the rate of what being transferred by any method?
Energy
What is the equation for power?
power= work divided time interval
What is the alternative form of power?
power=force X speed
What is the SI unit for power?
Watt, W
What is a watt defined as?
One joule per second
Work is done on an objects when what?
When a net force acts on the object to displace it in the direction of a component of the net force.
The amount of work done on an object by a force is equal to what?
The component of the force along the direction of motion times the distance the object moves.
Why do objects in motion have kinetic energy?
Because of their mass and speed
The net work done on or by an object is equal to what?
The change in the kinetic energy of the object
Potential energy is energy associated with an object's position. Two forms of potential energy discussed in this chapter are what?
Gravitational potential energy and elastic potential energy
Energy can change form but can never what?
Be created or destroyed.
Mechanical energy is the total kinetic and potential energy present in a given situation. True or false.
True
In the absence of friction, mechanical energy is conserved, so that what?
So that the amount of mechanical energy remains constant.
Power is the rate at which work is done or the rate of energy transfer. True or false
True
Machines with different power ratings do the same amount of work in different time intervals. True or false.
