Model Energy Transfer Between Objects - Physics
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What is the formula for energy transferred during a phase change at constant temperature?
What is the formula for energy transferred during a phase change at constant temperature?
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$Q=mL$. Latent heat $L$ is energy per unit mass for phase transitions.
$Q=mL$. Latent heat $L$ is energy per unit mass for phase transitions.
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What is the efficiency formula in terms of useful output energy and total input energy?
What is the efficiency formula in terms of useful output energy and total input energy?
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$\eta=\frac{E_{useful}}{E_{in}}$. Efficiency is always less than 1 due to energy losses.
$\eta=\frac{E_{useful}}{E_{in}}$. Efficiency is always less than 1 due to energy losses.
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What is the law of conservation of energy for energy transfer between objects?
What is the law of conservation of energy for energy transfer between objects?
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Total energy is constant; it only transfers or transforms. Energy cannot be created or destroyed in isolated systems.
Total energy is constant; it only transfers or transforms. Energy cannot be created or destroyed in isolated systems.
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What is the formula for heat transferred due to temperature change (no phase change)?
What is the formula for heat transferred due to temperature change (no phase change)?
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$Q=mc\Delta T$. Specific heat formula: $m$ is mass, $c$ is specific heat, $\Delta T$ is temperature change.
$Q=mc\Delta T$. Specific heat formula: $m$ is mass, $c$ is specific heat, $\Delta T$ is temperature change.
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What is the formula for thermal energy transferred during a phase change at constant temperature?
What is the formula for thermal energy transferred during a phase change at constant temperature?
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$Q=mL$. $m$ is mass and $L$ is latent heat of fusion or vaporization.
$Q=mL$. $m$ is mass and $L$ is latent heat of fusion or vaporization.
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What is the sign of $Q$ for an object that gains thermal energy from its surroundings?
What is the sign of $Q$ for an object that gains thermal energy from its surroundings?
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$Q>0$. Positive $Q$ means heat flows into the system.
$Q>0$. Positive $Q$ means heat flows into the system.
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What is the sign of $Q$ for an object that loses thermal energy to its surroundings?
What is the sign of $Q$ for an object that loses thermal energy to its surroundings?
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$Q<0$. Negative $Q$ means heat flows out of the system.
$Q<0$. Negative $Q$ means heat flows out of the system.
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What is the calorimetry condition for an isolated system of objects exchanging heat?
What is the calorimetry condition for an isolated system of objects exchanging heat?
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$\sum Q=0$. In isolation, total heat gained equals total heat lost.
$\sum Q=0$. In isolation, total heat gained equals total heat lost.
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Which energy transfer mechanism requires direct contact: conduction, convection, or radiation?
Which energy transfer mechanism requires direct contact: conduction, convection, or radiation?
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Conduction. Heat flows through materials via molecular collisions.
Conduction. Heat flows through materials via molecular collisions.
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Which energy transfer mechanism is heat transfer by bulk fluid motion: conduction, convection, or radiation?
Which energy transfer mechanism is heat transfer by bulk fluid motion: conduction, convection, or radiation?
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Convection. Heated fluid rises, cooler fluid sinks, creating circulation.
Convection. Heated fluid rises, cooler fluid sinks, creating circulation.
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Which energy transfer mechanism can occur through a vacuum: conduction, convection, or radiation?
Which energy transfer mechanism can occur through a vacuum: conduction, convection, or radiation?
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Radiation. Electromagnetic waves carry energy without a medium.
Radiation. Electromagnetic waves carry energy without a medium.
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What is the formula for work done by a constant force parallel to displacement?
What is the formula for work done by a constant force parallel to displacement?
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$W=Fd$. Force and displacement must be in same direction.
$W=Fd$. Force and displacement must be in same direction.
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What is the formula for gravitational potential energy change near Earth’s surface?
What is the formula for gravitational potential energy change near Earth’s surface?
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$\Delta U_g=mg\Delta h$. Near Earth, $g$ is constant at $9.8,\text{m/s}^2$.
$\Delta U_g=mg\Delta h$. Near Earth, $g$ is constant at $9.8,\text{m/s}^2$.
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What is the formula for kinetic energy of an object of mass $m$ moving at speed $v$?
What is the formula for kinetic energy of an object of mass $m$ moving at speed $v$?
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$K=\frac{1}{2}mv^2$. Energy of motion depends on mass and speed squared.
$K=\frac{1}{2}mv^2$. Energy of motion depends on mass and speed squared.
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What is the formula for power as energy transferred per unit time?
What is the formula for power as energy transferred per unit time?
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$P=\frac{\Delta E}{\Delta t}$. Power measures rate of energy transfer or transformation.
$P=\frac{\Delta E}{\Delta t}$. Power measures rate of energy transfer or transformation.
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Identify the correct unit for energy transfer (work or heat): $\text{W}$, $\text{J}$, or $\text{N}$.
Identify the correct unit for energy transfer (work or heat): $\text{W}$, $\text{J}$, or $\text{N}$.
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$\text{J}$. Joule is the SI unit for all forms of energy.
$\text{J}$. Joule is the SI unit for all forms of energy.
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Find $Q$ for $m=2,\text{kg}$, $c=500,\text{J/(kg,}^\circ\text{C)}$, $\Delta T=3^\circ\text{C}$.
Find $Q$ for $m=2,\text{kg}$, $c=500,\text{J/(kg,}^\circ\text{C)}$, $\Delta T=3^\circ\text{C}$.
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$Q=3000,\text{J}$. Using $Q=mc\Delta T$: $Q=2\times500\times^3=3000,\text{J}$.
$Q=3000,\text{J}$. Using $Q=mc\Delta T$: $Q=2\times500\times^3=3000,\text{J}$.
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Find the work done: a $10,\text{N}$ force acts $3,\text{m}$ in the same direction as motion.
Find the work done: a $10,\text{N}$ force acts $3,\text{m}$ in the same direction as motion.
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$W=30,\text{J}$. Using $W=Fd$: $W=10\times^3=30,\text{J}$.
$W=30,\text{J}$. Using $W=Fd$: $W=10\times^3=30,\text{J}$.
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Identify the direction of net heat transfer when two objects at $80^\circ\text{C}$ and $20^\circ\text{C}$ touch.
Identify the direction of net heat transfer when two objects at $80^\circ\text{C}$ and $20^\circ\text{C}$ touch.
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From $80^\circ\text{C}$ object to $20^\circ\text{C}$ object. Heat flows from hot to cold until thermal equilibrium.
From $80^\circ\text{C}$ object to $20^\circ\text{C}$ object. Heat flows from hot to cold until thermal equilibrium.
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Find $\eta$ if $E_{in}=200,\text{J}$ and $E_{useful}=50,\text{J}$ for a device.
Find $\eta$ if $E_{in}=200,\text{J}$ and $E_{useful}=50,\text{J}$ for a device.
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$\eta=0.25$. Using $\eta=\frac{E_{useful}}{E_{in}}$: $\eta=\frac{50}{200}=0.25$.
$\eta=0.25$. Using $\eta=\frac{E_{useful}}{E_{in}}$: $\eta=\frac{50}{200}=0.25$.
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What is the sign convention for heat $Q$ when energy enters an object as thermal energy?
What is the sign convention for heat $Q$ when energy enters an object as thermal energy?
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$Q>0$. Positive $Q$ means the system gains thermal energy from surroundings.
$Q>0$. Positive $Q$ means the system gains thermal energy from surroundings.
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What is the sign convention for work $W$ when work is done on an object by the surroundings?
What is the sign convention for work $W$ when work is done on an object by the surroundings?
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$W>0$. Positive $W$ means external forces add energy to the system.
$W>0$. Positive $W$ means external forces add energy to the system.
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State the first-law energy model relating internal energy change, heat, and work.
State the first-law energy model relating internal energy change, heat, and work.
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$\Delta U=Q+W$. First law states internal energy change equals heat plus work done on system.
$\Delta U=Q+W$. First law states internal energy change equals heat plus work done on system.
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What is the formula for kinetic energy of an object of mass $m$ and speed $v$?
What is the formula for kinetic energy of an object of mass $m$ and speed $v$?
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$K=\frac{1}{2}mv^2$. Energy of motion depends on mass and square of velocity.
$K=\frac{1}{2}mv^2$. Energy of motion depends on mass and square of velocity.
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What is the formula for gravitational potential energy change near Earth for height change $\Delta h$?
What is the formula for gravitational potential energy change near Earth for height change $\Delta h$?
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$\Delta U_g=mg\Delta h$. Work done against gravity equals weight times vertical displacement.
$\Delta U_g=mg\Delta h$. Work done against gravity equals weight times vertical displacement.
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What is the formula for thermal energy change of a substance with no phase change?
What is the formula for thermal energy change of a substance with no phase change?
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$Q=mc\Delta T$. Heat capacity $c$ relates temperature change to thermal energy gained.
$Q=mc\Delta T$. Heat capacity $c$ relates temperature change to thermal energy gained.
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Choose the correct transfer pathway: the Sun warming your skin through space uses which mechanism?
Choose the correct transfer pathway: the Sun warming your skin through space uses which mechanism?
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Radiation. Only electromagnetic waves can travel through vacuum of space.
Radiation. Only electromagnetic waves can travel through vacuum of space.
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Identify the sign of $Q$: a hot metal block cools while in contact with cooler water; what is $Q$ for the block?
Identify the sign of $Q$: a hot metal block cools while in contact with cooler water; what is $Q$ for the block?
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$Q<0$. Negative $Q$ means system loses thermal energy to surroundings.
$Q<0$. Negative $Q$ means system loses thermal energy to surroundings.
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Find the heat gained: $m=2,\text{kg}$, $c=500,\text{J/(kg\cdot ^\circ C)}$, $\Delta T=5,^\circ\text{C}$; what is $Q$?
Find the heat gained: $m=2,\text{kg}$, $c=500,\text{J/(kg\cdot ^\circ C)}$, $\Delta T=5,^\circ\text{C}$; what is $Q$?
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$5000,\text{J}$. Use $Q=mc\Delta T$: $(2)(500)(5)=5000,\text{J}$.
$5000,\text{J}$. Use $Q=mc\Delta T$: $(2)(500)(5)=5000,\text{J}$.
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Find the work done: a $10,\text{N}$ force pushes $3,\text{m}$ in the same direction; what is $W$?
Find the work done: a $10,\text{N}$ force pushes $3,\text{m}$ in the same direction; what is $W$?
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$30,\text{J}$. Apply $W=Fd$: $(10,\text{N})(3,\text{m})=30,\text{J}$.
$30,\text{J}$. Apply $W=Fd$: $(10,\text{N})(3,\text{m})=30,\text{J}$.
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