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Questions and Answers
Under what condition does the equation $W = Fd$ accurately calculate the work done on an object?
Under what condition does the equation $W = Fd$ accurately calculate the work done on an object?
- When the force and displacement are in the same direction. (correct)
- When the force is perpendicular to the displacement.
- When the force and displacement are in opposite directions.
- When the force is applied at a 45-degree angle to the displacement.
Which of the following best describes nonmechanical energy?
Which of the following best describes nonmechanical energy?
- Energy stored in a deformed elastic object.
- Energy that can dissipate from an object or system, such as heat or sound. (correct)
- Energy that is always conserved within a system.
- Energy associated with the motion of an object.
Which of the following is an example of a non-conservative force leading to the dissipation of mechanical energy into nonmechanical energy?
Which of the following is an example of a non-conservative force leading to the dissipation of mechanical energy into nonmechanical energy?
- The force exerted by a stretched rubber band.
- The elastic force of a spring.
- Gravity acting on a falling object in a vacuum.
- Friction between a sliding box and the floor. (correct)
What is the primary factor that determines gravitational potential energy?
What is the primary factor that determines gravitational potential energy?
What two factors determine the Elastic Potential Energy?
What two factors determine the Elastic Potential Energy?
A box is pushed across a rough horizontal surface. Which of the following is true regarding the work done by friction?
A box is pushed across a rough horizontal surface. Which of the following is true regarding the work done by friction?
How is work related to the change in kinetic energy of an object?
How is work related to the change in kinetic energy of an object?
What is the relationship between the force applied to an object, the object's displacement, and the work done, when the force is applied at an angle $\theta$ to the displacement?
What is the relationship between the force applied to an object, the object's displacement, and the work done, when the force is applied at an angle $\theta$ to the displacement?
Which of the following statements is true regarding the relationship between Kinetic Energy ($KE_i$) and ($KE_f$) when negative work is done on an object?
Which of the following statements is true regarding the relationship between Kinetic Energy ($KE_i$) and ($KE_f$) when negative work is done on an object?
How does the scientific definition of 'work' differ from the everyday definition?
How does the scientific definition of 'work' differ from the everyday definition?
Why is work considered a scalar quantity?
Why is work considered a scalar quantity?
A force is applied perpendicular to the displacement of an object. What can be said about the work done by this force?
A force is applied perpendicular to the displacement of an object. What can be said about the work done by this force?
What does the equation $P = \frac{W}{\Delta t}$ represent?
What does the equation $P = \frac{W}{\Delta t}$ represent?
How can power be expressed in terms of force and velocity?
How can power be expressed in terms of force and velocity?
If the net work done on an object is positive, what is the effect on the object's kinetic energy?
If the net work done on an object is positive, what is the effect on the object's kinetic energy?
What distinguishes kinetic energy from potential energy?
What distinguishes kinetic energy from potential energy?
Which of the following is true regarding the total energy of the universe?
Which of the following is true regarding the total energy of the universe?
A compressed spring is released, propelling a ball forward. Describe the energy transformation that takes place.
A compressed spring is released, propelling a ball forward. Describe the energy transformation that takes place.
An object is lifted to a certain height. What type of energy does the object gain?
An object is lifted to a certain height. What type of energy does the object gain?
A car accelerates from rest. Which of the following is the correct expression for calculating the change in kinetic energy ($\Delta KE$)?
A car accelerates from rest. Which of the following is the correct expression for calculating the change in kinetic energy ($\Delta KE$)?
Flashcards
When is Work Done?
When is Work Done?
Work is done when a force is applied for a displacement in the direction of that displacement.
Nonmechanical Energy
Nonmechanical Energy
Energy that can dissipate from an object or system (heat, light, sound, chemical).
Mechanical Energy
Mechanical Energy
Energy that can be conserved within an object or system.
Kinetic Energy
Kinetic Energy
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Potential Energy
Potential Energy
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Gravitational Potential Energy
Gravitational Potential Energy
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Elastic Potential Energy
Elastic Potential Energy
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Newtons
Newtons
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Joules
Joules
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Watts
Watts
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Total Energy
Total Energy
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Work and Acceleration
Work and Acceleration
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Work and Parallel Force
Work and Parallel Force
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Mechanical Energy
Mechanical Energy
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Power Definition
Power Definition
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Study Notes
- Work occurs when a force is applied causing displacement in the direction of the force, with the angle in the work equation representing the angle between them.
- If the force and displacement are in the same direction, cos(0) = 1 and work (W) = Fd.
- Total energy is always conserved in the universe.
Nonmechanical Energy
- Nonmechanical energy can dissipate from an object or system as heat, light, sound, or chemical energy.
- Nonconservative forces like friction and air resistance cause mechanical energy to dissipate, slowing objects down.
Mechanical Energy
- Mechanical energy can be conserved within an object or system.
Kinetic Energy
- Kinetic energy is associated with an object in motion with a nonzero speed.
- To determine if an object has Kinetic Energy, ask: Is it moving?
Potential Energy
- Potential energy is associated with an object due to its interaction with its environment.
Gravitational Potential Energy
- Gravitational potential energy is associated with an object's position relative to a gravitational source and it is defined relative to a zero level, such as the floor.
- To determine if an object has Gravitational Potential Energy, ask: Is it above the ground (or zero level)?
Elastic Potential Energy
- Elastic potential energy is stored in deformed elastic objects like compressed springs or stretched rubber bands.
- Elastic Potential Energy depends only on the spring constant k (N/m) and compression distance, not on mass.
- To determine if an object has Elastic Potential Energy, ask: Is there a spring or rubber band?
- Each type of energy depends only on the variables in its respective equation.
Units of Measurement
- Newtons (N) = kg * m / s²
- Newtons are the Unit of Force
- ∑F = ma
- Joules (J) = N * m
- Joules are the Unit of Energy and Work
- Wnet = Fd
- Watts (W) = J / s
- Watts are the Unit of Power
- P = W / Δt
- Work has two equations: W = Fdcosθ, which suggests work is caused by applying a force for a displacement in the direction of that displacement or Work–Kinetic Energy Theorem: W = ΔKE.
- The Work–Kinetic Energy Theorem suggests work causes a transfer of energy into or out of an object by changing its kinetic energy
- Since W = Fdcosθ and W = ΔKE, Fdcosθ = ΔKE.
- Mechanical Energy is the sum of Kinetic Energy and all forms of Potential Energy
- Work is a scalar that defines a transfer of energy, and can be negative or positive.
- A force only does work if a component of the force is parallel to the displacement of an object; a perpendicular force does no work (cos(90) = 0).
Power
- Power is defined by two equations: P = W / Δt = Fd / Δt = Fv.
- Power can also be written as P = ΔKE / Δt
Equations
- Formulas in parentheses will not be included on the test.
- Wnet = Fd cosθ (Sample Problem A)
- KE = (1/2)mv² (Sample Problem B)
- Wnet = ΔKE = (1/2)mvf² - (1/2)mvi² (Sample Problem C)
- PEg = mgh (Sample Problem D)
- PEelastic = (1/2)kx² (Sample Problem D)
- MEi = MEf = KE + ΣPE (Sample Problem E)
- P = W/Δt = Fv (Sample Problem F)
- F = mg
- Helpful Sample Problems
- SP. A: #1, 2, 18
- SP. D: #4 - 9
- SP. E: #10 - 14, 19 (See SP. B and D as well)
- SP. F: 15 - 17 (See SP. C as well for #17)
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