Kinetic & Potential Energy Explained

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Questions and Answers

How does increasing the height of an object affect its gravitational potential energy ($E_g$), assuming mass and acceleration due to gravity remain constant?

  • $E_g$ decreases linearly
  • $E_g$ remains unchanged
  • $E_g$ increases linearly (correct)
  • $E_g$ increases exponentially

A ball's kinetic energy ($E_k$) is 100 J. If the ball's velocity doubles while its mass remains constant, what is the new kinetic energy?

  • 300 J
  • 200 J
  • 100 J
  • 400 J (correct)

What is the relationship between kinetic energy ($E_k$) and mass ($m$) when velocity is constant?

  • Quadratic
  • Exponential
  • Inverse
  • Linear (correct)

Which of the following represents a transformation of energy, rather than a transfer?

<p>Charging a phone, converting electrical energy to chemical potential energy (B)</p> Signup and view all the answers

What type of energy is associated with the motion of an object?

<p>Kinetic (D)</p> Signup and view all the answers

A roller coaster car is at the top of a hill with a potential energy of 10,000 J. Assuming no energy loss due to friction, what is the kinetic energy of the car at the bottom of the hill?

<p>10,000 J (A)</p> Signup and view all the answers

A system has a total energy of 500 J. If the potential energy is 200 J, what is the kinetic energy?

<p>300 J (C)</p> Signup and view all the answers

According to the principles illustrated by the PhET skateboarder activity, what happens to the total energy of the system (skateboarder + ramp) when friction is present?

<p>Total energy remains constant even though kinetic and potential energy change. (B)</p> Signup and view all the answers

In the context of energy, which scenario best demonstrates the transformation of kinetic energy into thermal energy?

<p>A sled slowing down as it slides across a rough surface. (D)</p> Signup and view all the answers

How does the total energy of a system typically behave, assuming it's a closed system?

<p>Remains constant (C)</p> Signup and view all the answers

What are the units for gravitational potential energy?

<p>J (C)</p> Signup and view all the answers

If an object has a mass of 10 kg and is lifted to a height of 5 meters, what formula would you use to calculate the gravitational potential energy ($E_g$)?

<p>$E_g = mgh$ (B)</p> Signup and view all the answers

A 2 kg book is held 3 meters above the ground. What is its gravitational potential energy? (Assume $g = 9.8 m/s^2$)

<p>58.8 J (A)</p> Signup and view all the answers

A 5 kg object is moving at a velocity of 4 m/s. Calculate the kinetic energy ($E_k$) of the object.

<p>40 J (D)</p> Signup and view all the answers

An object's velocity increases from 2 m/s to 6 m/s. By what factor does its kinetic energy increase?

<p>9 (B)</p> Signup and view all the answers

What form of energy is stored in food?

<p>Chemical Potential (B)</p> Signup and view all the answers

A child is on a swing. At what point in the swing's motion is the gravitational potential energy the highest?

<p>At the highest point of the swing's arc. (D)</p> Signup and view all the answers

Which of the following is an example of kinetic energy being transformed into potential energy?

<p>A spring being compressed. (C)</p> Signup and view all the answers

A 5 kg object falls from a height of 10 meters. Just before it hits the ground, what form of energy does it primarily have?

<p>Kinetic energy. (B)</p> Signup and view all the answers

What remains constant when a ball is dropped from a height, assuming a closed system?

<p>The total energy of the ball. (B)</p> Signup and view all the answers

In the formula $E_g = mgh$, what does 'g' represent?

<p>Acceleration due to gravity (B)</p> Signup and view all the answers

An object moves from rest to a velocity of 5 m/s. If the object has a mass of 2 kg, what is its kinetic energy?

<p>25 J (B)</p> Signup and view all the answers

A pendulum swings from its highest point to its lowest point. What energy conversion is occurring?

<p>Potential energy to kinetic energy (A)</p> Signup and view all the answers

Why does total energy stay the same, according to the law of conservation of energy?

<p>Because energy cannot be created or destroyed (B)</p> Signup and view all the answers

What happens to a car's kinetic energy if its mass is doubled while its velocity remains constant?

<p>Kinetic energy is doubled (A)</p> Signup and view all the answers

Which of the following is an example of energy transfer?

<p>Heating soup on a stove (B)</p> Signup and view all the answers

A 2 kg object is dropped from a height of 5 meters. What is its potential energy at the top of its fall?

<p>98 J (A)</p> Signup and view all the answers

In a closed system, if the kinetic energy of an object decreases, what must happen to another form of energy in the system?

<p>It increases. (B)</p> Signup and view all the answers

What is the name for energy that is stored?

<p>Potential (C)</p> Signup and view all the answers

Which of the following units is equivalent to a Joule (J)?

<p>$kg \cdot m^2/s^2$ (C)</p> Signup and view all the answers

At which point on a roller coaster is kinetic energy usually at its maximum?

<p>Bottom of the highest hill (C)</p> Signup and view all the answers

Which factor does NOT affect an object's gravitational potential energy?

<p>Velocity (D)</p> Signup and view all the answers

What happens to total energy due to friction?

<p>Stays the same (C)</p> Signup and view all the answers

What unit is used to measure mass?

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

If an object's mass is 10 kg and it has a velocity of 2 m/s, what is its Kinetic Energy?

<p>20 J (B)</p> Signup and view all the answers

What are the 2 types of energy?

<p>Potential and Kinetic (B)</p> Signup and view all the answers

What happens to kinetic energy if mass doubles and so does velocity?

<p>energy times 8 (B)</p> Signup and view all the answers

At which location does a pendulum have the most potential energy?

<p>At the top of its swing (A)</p> Signup and view all the answers

Flashcards

Gravitational Potential Energy (Eg)

Energy an object has due to its position relative to a gravitational field. Affected by mass, gravity, and height.

Kinetic Energy (Ek)

Energy an object has due to its motion. Affected by mass and velocity.

Eg, m, g, and h relationship

The relationship between gravitational potential energy (Eg), mass (m), gravity (g), and height (h).

Ek, m, & v relationship

The relationship between kinetic energy (Ek), mass (m), and velocity (v).

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Transferred Energy

Energy that changes location or object, same form.

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Transformed Energy

Energy that changes form.

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Kinetic Energy Forms

Mechanical, heat, light, electric and sound.

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Potential Energy Forms

Chemical, gravitational potential, electric, and magnetic

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Law of Conservation of Energy

The total energy of an isolated system remains constant; energy is neither created nor destroyed but can change forms.

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Conservation of energy equation

The total mechanical energy (Ek + Eg) of a system remains constant if the only forces acting are conservative forces.

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Etotal

The total energy stays the same

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Energy Unit

Joules (J)

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Velocity Unit

meters/second (m/s)

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Acceleration Unit

meters/second^2 (m/s^2)

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Height Unit

meters (m)

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Mass Unit

kilograms (kg)

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Study Notes

  • Mass size and acceleration due to gravity determine the size of gravitational potential energy (Eg).
  • The higher the mass and velocity, the higher the kinetic energy (Ek).
  • The relationship between Eg, m, g, and h is linear/directly proportional.
  • The relationship between Ek, m & v: Ek and m are linear, so if m doubles, Ek doubles.
  • Ek and V are quadratic, so if V doubles, Ek quadruples.

Energy Transfer and Transformation

  • Transferred energy stays in the same form but moves locations.
  • Example: Heat transferring from hot to cold.
  • Transformed energy changes form.
  • Example: Charging a phone, electric energy becomes chemical potential energy.
  • Energy types: Kinetic (motion) and potential (storage).
  • Kinetic energy examples: mechanical, heat, light, electric, sound.
  • Potential energy examples: chemical (food, battery, explosives), gravitational potential, electric, magnetic.

Law of Conservation of Energy

  • Subtract or add energy values using the formulas: Ek + Eg = Etotal, Etotal - Eg = Ek, Etotal - Ek = Eg.
  • Determine the values of Eg or Ek using conservation of energy.

PhET Skateboarder Activity

  • The cat had the most Eg the higher up it was and the highest Ek when it was at the bottom of the ramp.
  • When the cat's mass was higher, Etotal was higher; when the cat's mass was smaller, the Etotal was also smaller.
  • When there is friction, the Ek transforms into thermal energy.
  • Even though all the different kinds of energy were changing on the bar graph, the Etotal stayed the same.
  • Create energy bar graphs for different situations.
  • Eg is height
  • Ek is speed
  • Et is friction/impact
  • Etotal stays the same the entire time, and in most scenarios, there will be 100 J total.

Energy Units

  • Energy measured in Joules (J): 1J = 1kgm²/s².
  • Velocity is measured in m/s.
  • Ek, Eg, Etotal measured in J.
  • Acceleration is measured in m/s².
  • Height is measured in meters (m).
  • Mass is measured in kg.

Calculations

  • Use Eg = mgh and Ek = ½ mv² to solve for any variable.
  • Read the problem and plug stuff into equation to solve.

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