Conservation of Energy - AP Physics C Mechanics

1. What happens to the kinetic energy of an object as it slows down?

   Decreases. Kinetic energy is proportional to velocity squared.

2. State the energy transformation when a ball is thrown up.

   Kinetic to potential energy. Moving upward converts kinetic energy to potential energy.

3. Calculate the potential energy of a 3 kg object at a height of 4 m. Use $g = 9.8 \text{ m/s}^2$.

   $117.6 \text{ J}$. Using $PE = mgh = (3)(9.8)(4) = 117.6$ J.

4. Calculate the kinetic energy of a 2 kg object moving at 3 m/s.

   $9 \text{ J}$. Using $KE = \frac{1}{2}mv^2 = \frac{1}{2}(2)(3)^2 = 9$ J.

5. What is the potential energy of a 5 kg object at 10 m height? Use $g = 9.8 \text{ m/s}^2$.

   $490 \text{ J}$. Using $PE = mgh = (5)(9.8)(10) = 490$ J.

6. What type of energy is present in a stationary object at a height?

   Potential energy. Energy due to position in gravitational field above reference level.

7. State the principle of conservation of mechanical energy.

   Total mechanical energy remains constant if only conservative forces act. No energy is lost when only conservative forces do work.

8. State the formula for kinetic energy.

   $KE = \frac{1}{2} mv^2$. Energy of motion, proportional to mass and velocity squared.

9. Which force is considered conservative in mechanical energy conservation?

   Gravitational force. Conservative forces allow energy to be recovered completely.

10. Find the velocity of a 2 kg ball with 8 J of kinetic energy.

    $2 \text{ m/s}$. Solving $8 = \frac{1}{2}(2)v^2$ gives $v = 2$ m/s.

11. State the energy change in a compressed spring.

    Potential to kinetic energy. Elastic potential energy converts to kinetic energy when spring extends.

12. What happens to mechanical energy when friction is present?

    Decreases. Friction converts mechanical energy to thermal energy.

13. What is the unit of energy in the International System of Units?

    Joule (J). Standard unit for all forms of energy in physics.

14. Identify the type of energy associated with an object's position.

    Potential energy. Energy stored due to position in a force field.

15. Which types of energy are involved in mechanical energy?

    Kinetic and potential energy. Mechanical energy is the sum of these two energy types.

16. What happens to potential energy as an object falls freely under gravity?

    Decreases. Potential energy converts to kinetic energy during free fall.

17. If mechanical energy is conserved, what can be said about energy loss to friction?

    No energy loss to friction. Energy conservation requires no dissipative forces like friction.

18. Calculate the height of a 4 kg object with 80 J of potential energy. Use $g = 10 \text{ m/s}^2$.

    $2 \text{ m}$. Solving $80 = (4)(10)h$ gives $h = 2$ m.

19. What is the effect of non-conservative forces on mechanical energy?

    Mechanical energy is not conserved. Non-conservative forces dissipate mechanical energy as heat or sound.

20. Does mechanical energy increase, decrease, or remain constant in a frictionless system?

    Remains constant. No non-conservative forces means energy is conserved.

21. Determine the mass of an object with 50 J potential energy at 5 m height. Use $g = 10 \text{ m/s}^2$.

    $1 \text{ kg}$. Solving $50 = m(10)(5)$ gives $m = 1$ kg.

22. What is the gravitational potential energy at Earth's surface?

    $0 \text{ J}$. Reference level for gravitational potential energy is typically ground level.

23. Find the height of a 2 kg object with 20 J potential energy. Use $g = 10 \text{ m/s}^2$.

    $1 \text{ m}$. Solving $20 = (2)(10)h$ gives $h = 1$ m.

24. Calculate the total mechanical energy of a system with 10 J kinetic and 15 J potential energy.

    $25 \text{ J}$. Total mechanical energy is the sum of kinetic and potential energies.

25. What happens to total mechanical energy in an isolated system?

    Remains constant. No external forces means energy cannot be created or destroyed.

26. What is the potential energy at the highest point of a pendulum swing?

    Maximum potential energy. At maximum height, all energy is potential with zero velocity.

27. What is the total mechanical energy of a system?

    Sum of kinetic and potential energy. Total mechanical energy equals $KE + PE$.

28. Calculate the velocity of a 4 kg object with 32 J of kinetic energy.

    $4 \text{ m/s}$. Solving $32 = \frac{1}{2}(4)v^2$ gives $v = 4$ m/s.

29. What is the kinetic energy of a 3 kg object moving at 0 m/s?

    $0 \text{ J}$. Zero velocity means zero kinetic energy by definition.

30. What is the effect of air resistance on mechanical energy?

    Reduces mechanical energy. Air resistance is a non-conservative force that dissipates energy.

31. Identify the formula for gravitational potential energy.

    $PE = mgh$. Energy due to position in gravitational field, proportional to height.

32. Find the kinetic energy of a 5 kg object moving at 2 m/s.

    $10 \text{ J}$. Using $KE = \frac{1}{2}mv^2 = \frac{1}{2}(5)(2)^2 = 10$ J.

33. State the energy change when a pendulum reaches its lowest point.

    Potential to kinetic energy. At lowest point, all energy is kinetic with maximum speed.

34. Find the potential energy of a 10 kg object at a height of 5 m. Use $g = 10 \text{ m/s}^2$.

    $500 \text{ J}$. Using $PE = mgh = (10)(10)(5) = 500$ J.

35. What is the energy transformation when an object falls from a height?

    Potential to kinetic energy. Gravitational potential energy converts to kinetic energy during fall.

36. Which type of energy is associated with an object's motion?

    Kinetic energy. Energy possessed by objects due to their motion or velocity.

37. What is the energy transformation principle in a freely falling object?

    Potential to kinetic energy. Gravitational potential energy converts to kinetic energy as object falls.

38. What is the kinetic energy of a 1 kg object at rest?

    $0 \text{ J}$. No motion means no kinetic energy present.

39. What is the general formula for conservation of mechanical energy?

    $E_{\text{initial}} = E_{\text{final}}$. States that initial total energy equals final total energy in isolated systems.

Study these flashcards