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Questions and Answers
Which of the following are characteristics of energy? (Select all that apply)
Which of the following are characteristics of energy? (Select all that apply)
A system is defined as:
A system is defined as:
In solving an energy problem, the environment is defined as:
In solving an energy problem, the environment is defined as:
A closed system:
A closed system:
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An open system
An open system
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In which of the following cases is positive work done by the applied force?
In which of the following cases is positive work done by the applied force?
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A book is held at a height of 2.0 m for 20 s by a librarian. How much work is done on the book by the librarian?
A book is held at a height of 2.0 m for 20 s by a librarian. How much work is done on the book by the librarian?
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A ball is swung around on a string, in uniform circular motion, covering a displacement of 2.0 m in 5.0 s. What is the work done on the ball by the string?
A ball is swung around on a string, in uniform circular motion, covering a displacement of 2.0 m in 5.0 s. What is the work done on the ball by the string?
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A 36.0 N force is applied to an object that moves 11.0 m in the same direction as the applied force on a frictionless surface. How much work is done on the object by the force?
A 36.0 N force is applied to an object that moves 11.0 m in the same direction as the applied force on a frictionless surface. How much work is done on the object by the force?
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A 36.0 N force is applied to an object that moves 11.0 m in the opposite direction of the applied force on a frictionless surface. How much work is done on the object by the force?
A 36.0 N force is applied to an object that moves 11.0 m in the opposite direction of the applied force on a frictionless surface. How much work is done on the object by the force?
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A 36 N force is applied to an object that remains stationary. How much work is done on the object by the applied force?
A 36 N force is applied to an object that remains stationary. How much work is done on the object by the applied force?
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A 40.0 N force pulls an object at an angle of 0 = 37.0° to its direction of motion. Its displacement is d = 8.00 m. How much work is done by the force on the object?
A 40.0 N force pulls an object at an angle of 0 = 37.0° to its direction of motion. Its displacement is d = 8.00 m. How much work is done by the force on the object?
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An object is pushed with an applied force of 36.0 N at an angle of 0 = 60.0° to the horizontal and it moves d = 10 m. What work does the force do on the object?
An object is pushed with an applied force of 36.0 N at an angle of 0 = 60.0° to the horizontal and it moves d = 10 m. What work does the force do on the object?
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What is wrong with this statement, "6 J of work is done"?
What is wrong with this statement, "6 J of work is done"?
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In which of the following cases is positive work done by an external force?
In which of the following cases is positive work done by an external force?
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A baseball pitcher throws a ball to the coach who catches it. Which of the following is a true statement about the work done by each person?
A baseball pitcher throws a ball to the coach who catches it. Which of the following is a true statement about the work done by each person?
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As an object falls, its KE always _____.
As an object falls, its KE always _____.
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What is the kinetic energy of a 12 kg object with a velocity of 10 m/s?
What is the kinetic energy of a 12 kg object with a velocity of 10 m/s?
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What is the mass of an object which has 2400 J of KE when traveling at 6.0 m/s?
What is the mass of an object which has 2400 J of KE when traveling at 6.0 m/s?
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A 3.0 kg object has 45 J of kinetic energy. What is its velocity
A 3.0 kg object has 45 J of kinetic energy. What is its velocity
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If the speed of a car is doubled, the KE of the car is:
If the speed of a car is doubled, the KE of the car is:
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Study Notes
PSI - Progressive Science Initiative
- PSI material is freely available for non-commercial use by students and teachers at www.njctl.org
- The site is not for commercial use without written permission from NJCTL
- NJCTL is an independent non-profit organization empowering teachers to improve schools for all students.
- NJCTL is supported by the New Jersey Education Association (NJEA)
Work and Energy (2024-10-27)
- Table of contents available at www.njctl.org for the Work and Energy presentation
- Sections include: System and Environment, Work, Kinetic Energy, Gravitational Potential Energy, Elastic Potential Energy, Conservation of Energy, GPE and Escape Velocity, and Power.
What is Energy?
- Energy is a fundamental concept described by Richard Feynman, a Nobel prize-winning physicist.
- Feynman stated that energy is a quantity that remains constant throughout the natural world's transformation.
- Feynman's work was primarily on mechanics, radiation, and heat, presented in 1963.
- Energy is as fundamental as space and time
- Energy is related to motion and forces.
System and Environment
- A system is a specific portion of the universe
- The environment is everything outside the system boundary.
- The system can be a particle, a group of particles, an object, an area or space.
- Define boundaries to isolate forces and matter in a system, to solve calculations with energy.
- If only internal forces are acting on a closed system, and no mass crosses the boundary, then the systems energy will remain un-changed.
- External forces and matter moving across the boundary changes the energy of the system.
- In solving problems, it is often possible to isolate a single object, or a small number of objects to calculate changes to Energy.
Closed System
- A system unaffected by anything in the environment
- Objects in the system cannot leave, nor can any outside object enter
- No outside forces affect anything inside the system
- Energy is neither transferred in nor out of the system
Open System
- A system that is affected by its environment.
- Objects in the system can leave it, and outside objects can enter it.
- Forces inside the system can affect the environment
- Energy can be transferred into or out from the system.
Work
- Work is the ability to increase or decrease the amount of energy at a given position-time in space.
- Work can change the motion of objects
- Work is measured in joules (J), which is the same unit as energy.
What is Work?
- Physics' work is different than common usage
- Work, by definition is the exertion of a force over a displacement where only the component of force in the direction of movement is taken into account
- If an object is held still, even if there is a force applied to the object, there is no work being done (no displacement).
Work Equation
- Work = Force x displacement cos θ
- θ is the angle between the force and displacement
Positive Work
- Work is positive when force and displacement are in the same direction
- Energy of the system increases
Negative Work
- Work is negative when force and displacement are in opposite directions
- Energy of the system decreases
Zero Work
- When an object moves perpendicularly to the direction of the force, or no movement occurs, the work is zero.
- Energy of the system remains unchanged
Two-Dimensional Forces and Work
- When a force is applied at an angle to the direction of displacement, resolve the force into components that are parallel and perpendicular to the displacement to determine the work done
- Only the parallel component affects work calculation
Vector Multiplication
- Many physics problems involve vectors (magnitude and direction)
- Summation and subtraction of such vectors often use trigonometry
- Multiplying vectors using scalars is also common in many physics problems
- Calculating work involves vector multiplication, frequently using the scalar dot product
Scalar Dot Product
- A scalar dot product of two vectors provides a scalar result
- Multiply the magnitude of the component of one vector that is aligned with the other vector times the magnitude of the second vector
- The maximum positive value for the dot product is when both vectors are aligned in the same direction
- The maximum negative value for the dot product is when both vectors are aligned in opposite directions
- Dot product equals zero when vectors are perpendicular
Kinetic Energy
- Kinetic energy is the energy of motion
- The equation of KE is 1/2 massvelocity squared
- Unit of measure is Joules (J)
Work-Kinetic Energy Equation
- If only constant external forces act in the same direction of the displacement, positive work is done
- The amount of work done results in a change of the energy (Kinetic) of an object
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Description
This quiz explores key concepts in work and energy, including kinetic energy, gravitational potential energy, and the conservation of energy. Designed for students, it offers insights into how energy transforms in natural systems. Prepare to test your understanding of fundamental energy principles!
