Conservation of Energy - AP Physics 1

1. State the formula for work done by a force.

   $W = F \times d \times \text{cos}(\theta)$. Work depends on force, displacement, and angle between them.

2. Calculate the work done by a 20 N force over 3 m at 0°.

   $W = 60 \text{ J}$. Using $W = Fd\cos(0°) = (20)(3)(1) = 60$ J.

3. Identify the energy transformation in a pendulum.

   Potential to kinetic and vice versa. Pendulum continuously exchanges kinetic and potential energy.

4. What is the energy form of a charged battery?

   Chemical potential energy. Energy stored in chemical bonds for later use.

5. Identify an example of a non-conservative force.

   Friction. Always opposes motion and converts mechanical energy to heat.

6. Identify the primary energy conversion in solar panels.

   Light to electrical energy. Photovoltaic cells convert sunlight into electrical energy.

7. Which energy transformation occurs when a ball is thrown upwards?

   Kinetic to potential energy. Ball slows down as it gains height, converting motion to position energy.

8. Calculate the elastic potential energy for $k = 200 \text{ N/m}$ and $x = 0.1 \text{ m}$.

   $PE = 1 \text{ J}$. Using $PE = \frac{1}{2}kx^2 = \frac{1}{2}(200)(0.1^2) = 1$ J.

9. State the energy conservation principle.

   Energy cannot be created or destroyed. First law of thermodynamics: energy is conserved in all processes.

10. Find the total mechanical energy if KE = 50 J and PE = 30 J.

    Total Energy = 80 J. Mechanical energy is the sum of kinetic and potential energies.

11. What is the energy transformation in a generator?

    Mechanical to electrical energy. Converts rotational motion into electrical energy output.

12. What is the energy conversion in a hydroelectric dam?

    Potential to kinetic to electrical energy. Water falls, spins turbines, generates electricity.

13. Find the kinetic energy of a 3 kg object moving at 4 m/s.

    $KE = 24 \text{ J}$. Using $KE = \frac{1}{2}mv^2 = \frac{1}{2}(3)(4^2) = 24$ J.

14. Find the gravitational potential energy of a 5 kg object 10 m high.

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

15. State what happens to energy in inelastic collisions.

    Mechanical energy is not conserved. Some kinetic energy converts to heat and sound.

16. Find the mechanical energy if a system has 100 J of KE and 200 J of PE.

    Mechanical Energy = 300 J. Sum of kinetic and potential energies in the system.

17. Define the Conservation of Mechanical Energy.

    Total mechanical energy is constant if only conservative forces act. When only gravity and springs act, $KE + PE$ stays constant.

18. What is the energy form of light emitted by a bulb?

    Radiant energy. Electromagnetic energy in the form of visible light waves.

19. Calculate total energy if a 5 kg object at 10 m has 200 J KE.

    Total Energy = 690 J. Using $PE = mgh = (5)(9.8)(10) = 490$ J, total = $200 + 490 = 690$ J.

20. Identify the energy form of a moving car.

    Kinetic energy. Energy due to motion of the vehicle.

21. Calculate power if 60 J is used in 3 seconds.

    Power = 20 W. Using $P = \frac{W}{t} = \frac{60}{3} = 20$ W.

22. Identify the type of force that conserves mechanical energy.

    Conservative force. Forces like gravity where work is path-independent.

23. What does it mean for a force to be non-conservative?

    Energy is not conserved; work depends on path. Work depends on path taken; mechanical energy decreases.

24. What is the relationship between work and energy?

    Work is a transfer of energy. Work transfers energy from one system to another.

25. What is the unit of energy in the International System?

    Joule. Standard SI unit for all forms of energy and work.

26. What is the formula for power in terms of work?

    $P = \frac{W}{t}$. Power equals work done divided by time taken.

27. Find the increase in KE if work done is 150 J.

    Increase in KE = 150 J. Work-energy theorem: work done equals change in kinetic energy.

28. What is the unit of power in the International System?

    Watt. Standard SI unit for power (energy per unit time).

29. Calculate potential energy of a 2 kg object at height 6 m.

    $PE = 117.6 \text{ J}$. Using $PE = mgh = (2)(9.8)(6) = 117.6$ J.

30. What is the energy form of a wound-up clock spring?

    Elastic potential energy. Energy stored by winding the spring mechanism.

31. What is the potential energy formula for a spring?

    $PE = \frac{1}{2}kx^2$. Energy stored in compressed or stretched springs.

32. What happens to total energy in an isolated system?

    It remains constant. Energy can only be transformed, never created or destroyed.

33. Identify the energy form of a compressed spring.

    Elastic potential energy. Energy stored when spring is compressed or stretched.

34. Calculate work if a 50 N force moves an object 4 m at 60°.

    $W = 100 \text{ J}$. Using $W = Fd\cos(60°) = (50)(4)(0.5) = 100$ J.

35. Find and correct the error: 'Energy is lost in a closed system.'

    Correct: 'Energy is transformed, not lost.'. Energy is conserved in closed systems, only transformed.

36. What is the formula for kinetic energy?

    $KE = \frac{1}{2}mv^2$. Energy of motion depends on mass and velocity squared.

37. Find the power if 300 J is used in 10 seconds.

    Power = 30 W. Using $P = \frac{W}{t} = \frac{300}{10} = 30$ W.

38. What is the formula for gravitational potential energy?

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

39. Define power in terms of energy.

    Power is the rate of energy transfer. How quickly energy is transferred or transformed.

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