Physics Work-Energy Theorem and Mechanical Energy

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Questions and Answers

What is the ability to do work called?

  • Energy (correct)
  • Mass
  • Power
  • Force

Who discovered the relationship between heat and mechanical energy?

  • James Prescott Joule (correct)
  • Isaac Newton
  • Albert Einstein
  • Lord Kelvin

When lifting a box, what kind of energy does it gain?

  • Thermal Energy
  • Mechanical Energy
  • Kinetic Energy
  • Gravitational Potential Energy (correct)

What formula represents Kinetic Energy?

<p>KE = ½ mv^2 (B)</p> Signup and view all the answers

How is work calculated in relation to gravitational potential energy?

<p>W = ∆ PE g = (mgh f – mgh o) (D)</p> Signup and view all the answers

What unit is energy measured in?

<p>Joules (A)</p> Signup and view all the answers

What does the term 'Mechanical Energy' refer to?

<p>The energy of an object due to its motion or position (C)</p> Signup and view all the answers

What happens to the work done when an object is raised higher?

<p>It increases with the height raised (B)</p> Signup and view all the answers

What does it mean for gravitational potential energy to be path-independent?

<p>It remains constant as long as the straight-line distance to the ground is the same. (D)</p> Signup and view all the answers

How can kinetic energy (KE) be calculated?

<p>By using the equation $KE = \frac{1}{2}mv^2$. (B)</p> Signup and view all the answers

What does the work-energy theorem state?

<p>The work done is equal to the change in kinetic energy plus change in potential energy. (B)</p> Signup and view all the answers

What happens when negative work is done on a system?

<p>Energy is lost from the system. (D)</p> Signup and view all the answers

If an object is at rest, what can be said about its kinetic energy?

<p>It has no kinetic energy. (C)</p> Signup and view all the answers

What is the relationship between force and acceleration in Newton's second law?

<p>Force is equal to acceleration times mass. (C)</p> Signup and view all the answers

What is the significance of the equation $V_f^2 - V_o^2 = 2ad$?

<p>It relates velocity to acceleration and distance. (D)</p> Signup and view all the answers

How is gravitational potential energy (PE) defined?

<p>It is dependent on both mass and height relative to a reference point. (A)</p> Signup and view all the answers

Flashcards

Gravitational Potential Energy (GPE)

The amount of energy an object possesses due to its position in a gravitational field. It is independent of the path taken to reach that position.

Work-Energy Theorem

The work done on an object is equal to the change in the object's kinetic energy.

Kinetic Energy (KE)

Energy possessed by an object due to its motion.

Acceleration (a)

The rate of change of an object's velocity. It is calculated by dividing the change in velocity by the time taken for the change.

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Momentum (p)

The product of mass and velocity. It is a measure of the object's momentum.

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Work (W)

A force applied over a distance.

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Inertia

The tendency of an object to resist changes in motion.

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Gravity

A force that pulls objects towards the center of the Earth.

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What is energy?

The ability to do work.

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Kinetic energy

The energy an object possesses due to its motion.

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Potential energy

The energy an object possesses due to its position.

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Gravitational potential energy formula

The formula for calculating gravitational potential energy: PEg = mgh.

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What does energy have to do with work?

It's the ability to do work.

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Work-energy theorem and kinetic energy

The work-energy theorem states that the work done on an object is equal to the object's change in kinetic energy.

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Study Notes

Work-Energy Theorem

  • The ability to do work is called energy.
  • Energy is measured in Joules (J).
  • James Prescott Joules, a physicist, discovered the relationship between heat and mechanical energy.
  • This led to the Law of Conservation of Energy and the First Law of Thermodynamics.
  • Work done on an object can result in a change in its energy.

Mechanical Energy

  • Mechanical energy is the energy (ability to do work) of an object due to its:

    • Motion
    • Position

  • Kinetic Energy (KE): This is energy due to motion, calculated as KE = ½mv². (m = mass, v = velocity)

  • Gravitational Potential Energy (PEg): This is energy due to position in a gravitational field, calculated as PEg = mgh. (m = mass, g = acceleration due to gravity, h = height)

Work's Relation to Gravitational Potential Energy

  • Work (W) is force (F) multiplied by the distance (d) over which the force is applied (W=Fd).

  • Change in gravitational potential energy (ΔPEg) is equal to the work done by gravity (W = ΔPEg = (mg)(hf - h0)).

    • (hf = final height, h0 = initial height)

  • The change in potential energy of an object is directly related to the work done by gravity on the object.

Which Objects Have the Highest/Lowest Kinetic Energy?

  • The object higher up on a staircase has higher gravitational potential energy initially, but lower kinetic energy compared to the object that is rolling down the staircase.
  • The object closest to the ground has the lowest potential energy compared to the objects that are at higher points.

Gravitational Potential Energy is Path-Independent

  • The path taken by an object doesn't affect its change in gravitational potential energy, as long as the starting and ending heights are the same.

Work's Relation to Kinetic Energy

  • Work (W) equals the change in kinetic energy (ΔKE), calculated as W = ΔKE = KEf - KE0 = ½mv²f - ½mv²0.
    • (KEf = final kinetic energy, KE0 = initial kinetic energy, vf = final velocity, v0 = initial velocity)

Kinetic Energy (KE) Calculation

  • Kinetic energy can also be calculated using the equation: KE = p²/2m, where p is momentum and m is mass.

Summary - Equations

  • All relevant equations are in the document.

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