Physics Chapter 6: Work and Energy
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Questions and Answers

What is the definition of energy in the context of physics?

  • The ability to consume fuel.
  • The amount of force exerted on an object.
  • The total capacity of all devices in a society.
  • The ability for an object or system to perform work. (correct)

    • Which of the following statements correctly describes when work is done?

  • Work is done if a force is applied with no change in motion.
  • Work is done when a force acts on an object and there is displacement. (correct)
  • Work is done when an object remains at rest.
  • Work is done regardless of the direction of the force.

    • According to the Law of inertia, what is true about objects at rest or moving at constant velocity?

  • They are in a constant energy state that allows for immediate work.
  • They prefer to stay in their current state until acted upon by a force. (correct)
  • They require no force to change their state of motion.
  • They will naturally accelerate if no force acts on them.

    • What happens if no force is applied to an object in terms of work?

    <p>No work is done as there is no change in motion.</p> Signup and view all the answers

    What must occur for work to be done on an object?

    <p>There must be a force and a displacement in the direction of the force.</p> Signup and view all the answers

    What does the conservation law state about energy?

    <p>Energy can only change forms.</p> Signup and view all the answers

    In an isolated system, what happens to the total energy?

    <p>It remains constant.</p> Signup and view all the answers

    Which of the following statements about power is true?

    <p>Power is the rate at which work is performed.</p> Signup and view all the answers

    What unit is used to measure power?

    <p>Watt</p> Signup and view all the answers

    Which device converts electrical energy into light and heat?

    <p>Light bulb</p> Signup and view all the answers

    How is efficiency best described?

    <p>The quality of energy conversion to useful work.</p> Signup and view all the answers

    To calculate power, which of the following formula is correct?

    <p>Power = Work / Time</p> Signup and view all the answers

    What is one way energy is transformed in a car engine?

    <p>Chemical energy into mechanical energy.</p> Signup and view all the answers

    What is the formula for calculating kinetic energy?

    <p>KE = 1/2 mv^2</p> Signup and view all the answers

    If an object has a kinetic energy of 225 J and a mass of 15 kg, what is its speed?

    <p>15 m/s</p> Signup and view all the answers

    What is the relationship between gravitational potential energy, mass, and height?

    <p>GPE increases as either mass or height increases</p> Signup and view all the answers

    What is the gravitational potential energy of a 5 kg object raised to a height of 15 m?

    <p>750 J</p> Signup and view all the answers

    What is the weight of a 75 kg person on Earth?

    <p>750 N</p> Signup and view all the answers

    If a 39,000 kg boat has a kinetic energy of 52,000 J, what is its velocity?

    <p>4 m/s</p> Signup and view all the answers

    How much potential energy does an object gain if it is lifted 3 meters with a weight of 37 N?

    <p>111 J</p> Signup and view all the answers

    What will happen to the gravitational potential energy if the mass of an object is doubled while the height remains constant?

    <p>It doubles</p> Signup and view all the answers

    What is the formula for kinetic energy?

    <p>$KE = \frac{1}{2}mv^2$</p> Signup and view all the answers

    How does doubling the mass of an object affect its kinetic energy?

    <p>It doubles</p> Signup and view all the answers

    If the speed of an object is tripled, how does its kinetic energy change?

    <p>It increases by a factor of nine</p> Signup and view all the answers

    Which statement is true regarding kinetic energy and speed?

    <p>Kinetic energy increases as speed increases.</p> Signup and view all the answers

    Which object would have the highest kinetic energy if both are moving at the same speed?

    <p>A 3 kg object</p> Signup and view all the answers

    What happens to the kinetic energy of an object if it becomes stationary?

    <p>It decreases to zero</p> Signup and view all the answers

    When comparing two objects of different masses but the same speed, what can be concluded about their kinetic energies?

    <p>The object with greater mass has more kinetic energy.</p> Signup and view all the answers

    What is the effect of increasing both mass and speed on kinetic energy?

    <p>Kinetic energy increases significantly.</p> Signup and view all the answers

    What is the power of an engine that performs 30,000 J of work in 20 seconds?

    <p>1,500 W</p> Signup and view all the answers

    What does the term efficiency indicate regarding a machine's performance?

    <p>The ratio of useful energy output to energy input</p> Signup and view all the answers

    If a car engine performs 750 J of work using 5000 J of energy, what is its efficiency?

    <p>15%</p> Signup and view all the answers

    A construction worker transfers 8.0 J of energy into driving a nail using 20 J exerted. What is the efficiency of the hammering?

    <p>40%</p> Signup and view all the answers

    Which of the following is NOT a reason for energy loss in machines?

    <p>Kinetic energy</p> Signup and view all the answers

    What expression is used to calculate efficiency?

    <p>$\frac{Work\ performed}{Energy\ consumed} \times 100%$</p> Signup and view all the answers

    Which of the following statements is true about the efficiency of any machine?

    <p>Efficiency is always less than 100%</p> Signup and view all the answers

    In a power generation scenario, if an engine has an output power of 2000 W and runs for 10 seconds, how much work did it perform?

    <p>20,000 J</p> Signup and view all the answers

    If a force of 10N is applied to move an object over a distance of 5m, how much work is done?

    <p>50 Nm</p> Signup and view all the answers

    Which scenario illustrates an example where work is done?

    <p>Lifting a box from the floor</p> Signup and view all the answers

    What is the average force exerted by a plane if it performs 50,000,000 J of work over a distance of 2,000m?

    <p>50,000 N</p> Signup and view all the answers

    How much work is done if 0N of force is applied over a distance of 5m?

    <p>0 Nm</p> Signup and view all the answers

    Which of the following correctly represents the work formula?

    <p>W = F × d</p> Signup and view all the answers

    If a student pushes against a wall with a force of 200N but the wall does not move, how much work does the student do?

    <p>0 Nm</p> Signup and view all the answers

    A car engine exerts a force of 2500 N and does 100,000 J of work. What is the distance the car moves?

    <p>25 m</p> Signup and view all the answers

    If I apply a constant force of 15N and the object travels 4m, what is the work done?

    <p>60 J</p> Signup and view all the answers

    Study Notes

    Chapter 6: Work and Energy

    • Work is defined as the ability of an object or system to perform work.

    • Work is done when a force is exerted on an object and the object moves a distance in the direction of the force.

    • Work = Force × Distance

    • The SI unit of work is the Joule (J), which is equal to 1 Newton-meter (N⋅m).

    • Work is only done when the object moves in the direction of the force.

    Energy

    • Energy is the capacity to do work.

    • Individuals use devices and tools that consume energy.

    • Examples of devices and tools that consume energy include refrigerators, lights, cars, trucks, planes, trains, and mobile phones.

    • Humans also consume energy through food.

    • Society's advancement can be measured by its energy consumption.

    Kinetic Energy

    • Kinetic energy is the energy of motion of an object.

    • Kinetic energy depends on the speed of the object and its mass.

    • Kinetic Energy = 1/2 × mass × speed² (KE=1/2×m×v²)

    • If two objects have the same mass, then the faster object has more kinetic energy. If two objects have the same speed, the more massive object has more kinetic energy.

    Potential Energy

    • Potential energy is energy that is stored and waiting to be used later.

    • Gravitational potential energy is the energy of an object due to its position in a gravitational field

    • Gravitational Potential Energy = mass × gravitational field strength × height (GPE=mgh).

    • Fg = mg where g = 10 m/s² is the acceleration of gravity.

    • The force of gravity is the force of an object acting on the surface of Earth.

    Conservation of Energy

    • Matter and energy are neither created nor destroyed, just transformed from one form to another, or from one object to another.

    • If a system does not interact with its environment (isolated system), then its total energy remains constant.

    • The conservation of energy is analogous to the law of inertia: the motion of an isolated object or system does not change.

    Power & Efficiency

    • Power is the rate at which work is done, or the rate at which energy is used.

    • Power is measured in Watts (W), where 1 W = 1 J/s.

    • Power = Work / time (P=W/t).

    • Efficiency is the ratio of the useful work output to the total energy input, expressed as a percentage.

    • Efficiency= output work / input energy × 100%

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    Related Documents

    Chapter 6: Work and Energy Physics 100 Lecture Notes PDF

    Description

    Dive into the concepts of work and energy in this quiz based on Chapter 6. Explore how work is done, the relationship between work and energy, and understand kinetic energy. Test your knowledge of these fundamental principles in physics.

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