Physics Chapter 5 - Work & Energy Flashcards

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Questions and Answers

What is work?

A force that causes a displacement of an object.

Work is equal to the magnitude of the force, F, times the magnitude of the displacement. Formula: W = ______

What determines whether work is done on an object?

The object must be moved because of the action of a force.

How is work related to the direction of the displacement?

Work is done only when components of a force are parallel to the displacement. Signup and view all the answers

The formula for net work done by a constant net force is Wnet = Fnet d cos______

θ Signup and view all the answers

What units are used to measure work?

Newtons times meters (N×m) or joules (J). Signup and view all the answers

Can work be positive or negative?

True Signup and view all the answers

How does work that changes an object's speed affect whether the work is positive or negative?

If net work is positive, the object speeds up; if negative, it slows down. Signup and view all the answers

What is kinetic energy?

Energy associated with an object in motion. Signup and view all the answers

The formula for kinetic energy is KE = ______

1/2 mv² Signup and view all the answers

How is kinetic energy measured?

In joules (J). Signup and view all the answers

How is kinetic energy related to an object's speed and mass?

It depends on both speed and mass; more mass means more kinetic energy at the same speed. Signup and view all the answers

The Work-Kinetic Energy Theorem states Wnet = ______

∆KE Signup and view all the answers

How does a moving hammer use its energy upon striking a nail?

Part of the energy drives the nail, and part warms the hammer and nail. Signup and view all the answers

What is potential energy?

Stored energy present in an object due to its position. Signup and view all the answers

What is gravitational potential energy?

Energy associated with an object's position relative to a gravitational source. Signup and view all the answers

The formula for gravitational potential energy is PEg = ______

mgh Signup and view all the answers

How is gravitational potential energy measured?

In joules (J). Signup and view all the answers

How is height measured for gravitational potential energy?

Relative to some zero level. Signup and view all the answers

What is elastic potential energy?

Energy stored in any compressed or stretched object. Signup and view all the answers

What is the relaxed length of a spring?

The length of the spring with no external forces acting on it. Signup and view all the answers

How does elastic potential energy get into a spring?

By compressing or stretching the spring with an external force. Signup and view all the answers

The formula for elastic potential energy is PEelastic = ______

1/2 kx² Signup and view all the answers

Study Notes

Work

Work occurs when a force causes an object to move, defined as either the force applied or the distance over which it acts.
The formula for work is W = Fd, where W is work, F is the force, and d is the displacement.
Work is only done when the object is displaced due to the applied force; mere application of force without movement does not count as work.

Work and Direction

For work to be done, the force must have a component parallel to the object's displacement; perpendicular components do not do work.
Net work done by a constant force can be calculated with the formula W_net = F_net × d × cos(θ), incorporating the angle θ between force and displacement.

Measurement and Properties of Work

Work is measured in units of newton-meters (N×m), equivalent to joules (J).
Work can be positive or negative: positive work occurs when force and displacement are in the same direction, while negative work occurs when they are in opposite directions.

Kinetic Energy

Kinetic energy (KE) is the energy of an object in motion.
The formula for kinetic energy is KE = 1/2 mv², where m is mass and v is speed.
Kinetic energy is also measured in joules (J) and varies with an object's mass and speed. A heavier object at the same speed has more kinetic energy.

Work-Kinetic Energy Theorem

The Work-Kinetic Energy Theorem states that the net work done on an object equals the change in its kinetic energy: W_net = ∆KE.
When a hammer strikes a nail, part of the energy drives the nail while some energy is converted to heat due to impact.

Potential Energy

Potential energy (PE) is stored energy due to an object's position or configuration.
Gravitational potential energy is associated with an object's position relative to a gravitational source, measured by the formula PE_g = mgh, where h is the height.

Measurement of Potential Energy

Gravitational potential energy is measured in joules (J) and depends on the chosen reference height, typically ground level.
Elastic potential energy is stored in objects like springs when they are compressed or stretched, expressed by the formula PE_elastic = 1/2 kx², where k is the spring constant and x is the displacement from its relaxed length.

Elastic Potential Energy

The relaxed length of a spring is its length when no external force is acting. Elastic potential energy is stored when the spring is compressed or stretched beyond this length.

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Test your knowledge with these flashcards on Work and Energy from Physics Chapter 5. Each card covers key concepts, definitions, and principles related to the work-energy principle. Perfect for quick revision or deeper understanding of the topic.