3.3 - Work, Energy and Power Flashcards
What is work done? What is the equation?
The work done, or energy transferred, is the product of the force and the distance moved by the force in the direction of movement. Equation: W = F × d (where d is the distance moved by the force).
What is work done measured in?
Joules (J), which is the unit of energy.
What is the definition of a joule?
One joule is equal to the work done when a force of 1 Newton causes an object to move 1 meter in the direction of the force.
What formula is used for work done when the force is acting at an angle to the direction it’s moving in?
Equation: W = F × cos(ϴ) × d. The component of force in the same direction as movement (Fcosϴ) is multiplied by the distance moved. Important: Always find the component parallel to the direction of motion.
What is a closed system?
A closed system is any system in which all energy transfers are accounted for. Energy or matter cannot enter or leave a closed system.
What is the principle of conservation of energy?
The total energy of a closed system remains constant. Energy can neither be created nor destroyed, only transferred from one form to another.
What is energy simply known as?
The capacity to do work.
What is the energy transfer occurring in a car engine?
Chemical energy (fuel) is converted into kinetic energy.
What energy is gained when a cyclist rides up a mountain?
Gravitational potential energy.
Name some types of energy.
Kinetic, gravitational potential, thermal, elastic potential, chemical, nuclear, electrical, sound, and light energy.
What is kinetic energy?
The energy of an object due to its movement.
What is the formula for kinetic energy?
Equation: KE = 0.5mv² (where m = mass and v = velocity).
How do you derive the formula for kinetic energy from first principles?
KE = Work done = Force × Distance → KE = ma × d. Using suvat: v² = u² + 2as → as = 0.5(v² - u²). Substituting as for ad: KE = 0.5m(v² - u²). If u = 0, then KE = 0.5mv².
What is an object’s gravitational energy?
Gravitational potential energy (Ep) is the energy an object has due to its position in a uniform gravitational field. The greater the height, the greater the gravitational potential energy.
What is the formula for gravitational potential energy in a uniform gravitational field?
Equation: Ep = mgΔh (where m = mass, g = acceleration due to gravity, and Δh = change in height).
How do you derive the equation for gravitational potential energy?
GPE = Work done = Force × Distance. The force required to lift an object = its weight (mg). Distance moved = change in height (Δh). Ep = mgΔh.
What is a common example of energy transfer between kinetic and gravitational potential energy?
A swinging pendulum.
What happens to energy in a swinging pendulum (ignoring drag forces)?
Loss in potential energy = Gain in kinetic energy (and vice versa).
What equation allows you to calculate the velocity of an object that has fallen from rest through a height Δh?
Equation: V = √(2gΔh), derived from KE = GPE → 0.5mv² = mgΔh. Canceling mass (m) and rearranging gives V = √(2gΔh).
What is the formula for power?
Equation: Power = Work done / Time. Power is defined as the rate of doing work or transferring energy.
What is power measured in?
Watts (W) or Joules per second (J/s).
What unit of power is commonly used in daily life?
Kilowatts (kW), where 1 kW = 1000 W.
What is another equation for power related to a moving object?
Equation: P = F × V (where F = Force and V = Velocity of the object).
How do you derive P = Fv from first principles?
Work done = Force × Distance → Power = Work done / Time → P = (F × d) / t. Since distance / time = speed, we get P = Fv.
What formula should be used for power if the force and motion are in different directions?
Equation: P = Fvcosϴ.
Can you ever have a 100% energy transfer?
No. Energy transfers always involve losses (usually as heat or friction). Nothing can ever be 100% efficient.
What is the equation for efficiency?
Equation: Efficiency = (Useful output energy / Total input energy) × 100.
What is efficiency a measure of?
A measure of how well a device converts input energy into the desired useful output energy.
What type of diagram is commonly used to represent efficiency/power problems?
Sankey diagrams (diagrams with arrows showing energy transfers).
Name a device where the small amount of lost energy is actually useful.
Potential answers include electric heaters, incandescent light bulbs, etc.
