Physics Chapter 9 Flashcards

Questions and Answers

In physics, work is defined as

force times distance

If you lift two loads up one story, how much work do you do compared to lifting just one load up one story?

Less

The same amount

Half as much

Twice as much (correct)

If you lift one load up two stories, how much work do you do compared to lifting one load up only one story?

The same amount

Less

Twice as much (correct)

Half as much

If Nellie Newton pushes an object with twice the force for twice the distance, she does

Four times the work Signup and view all the answers

The unit of work is the

Joule Signup and view all the answers

Power is defined as the

Work done on an object divided by the time taken Signup and view all the answers

The unit of power is the

Watt Signup and view all the answers

Potential energy is the energy an object has because of its

Location Signup and view all the answers

The amount of potential energy possessed by an elevated object is equal to

The work done in lifting it Signup and view all the answers

Kinetic energy of an object is equal to

One half the product of its mass times its speed squared Signup and view all the answers

How much farther will a car traveling at 100 km/s skid than the same car traveling at 50 km/s?

Four times as far Signup and view all the answers

An arrow in a bow has 70 J of potential energy. Assuming no loss of energy to heat, how much kinetic energy will it have after it has been shot?

70 J Signup and view all the answers

Energy is changed from one form to another with no net loss or gain.

True Signup and view all the answers

As a pendulum swings back and forth

All of the above Signup and view all the answers

When a car's speed triples, its kinetic energy

Increases by nine times Signup and view all the answers

Rockets are launched from an airplane in the forward direction of motion. The kinetic energy of the airplane will be

Decreased Signup and view all the answers

A job is done slowly, and an identical job is done quickly. Both jobs require the same amount of work but different amounts of

Power Signup and view all the answers

Which requires more work: lifting a 70-kg sack vertically 2 meters or lifting a 35-kg sack vertically 4 meters?

Both require the same amount of work Signup and view all the answers

A ball is thrown into the air with 100 J of kinetic energy which is transformed to gravitational potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance, its kinetic energy is

Less than 100 J Signup and view all the answers

An object that has kinetic energy must be

Moving Signup and view all the answers

An object that has kinetic energy must have

Momentum Signup and view all the answers

Which has greater kinetic energy, a car traveling at 30 km/h or a half-as-massive car traveling at 60 km/h?

The 60 km/h car Signup and view all the answers

A person on a roof throws one ball downward and an identical ball upward at the same speed. The ball thrown downward hits the ground with 140 J of kinetic energy. Ignoring air friction, with how much kinetic energy does the second ball hit the ground?

140 J Signup and view all the answers

An object at rest may have

Potential energy Signup and view all the answers

If an object has kinetic energy, then it also must have

Energy Signup and view all the answers

If the velocity of a moving object doubles, then what else doubles?

Momentum Signup and view all the answers

All simple machines ideally work on the principle that

Work input equals work output Signup and view all the answers

About how efficient is a typical gasoline-burning car engine?

30% Signup and view all the answers

A small economy car (low mass) and a limousine (high mass) are pushed from rest across a parking lot, equal to distances with equal forces. The car that receives more kinetic energy is the

Neither one - they receive the same amount of kinetic energy Signup and view all the answers

A popular toy consists of an aligned row of identical elastic balls suspended by strings so they touch each other. When two balls on one end are elevated and released, they slam into the array of balls and two balls pop out the other side. If instead, one ball popped out with twice the speed, this would be a violation of the conservation of

Energy Signup and view all the answers

Consider molecules of hydrogen gas and molecules of heavier oxygen gas that have the same kinetic energy. The molecules with the greater speed are

Hydrogen Signup and view all the answers

Study Notes

Work and Energy Concepts

Work is defined as force multiplied by distance.
Lifting two loads to one story requires twice the work compared to lifting one load.
Lifting one load up two stories requires twice the work compared to lifting it one story.
Applying twice the force over twice the distance results in four times the work done.

Units of Measurement

The standard unit of work is the joule (J).
Power is defined as the work done divided by the time taken, with the unit of power being the watt (W).

Types of Energy

Potential energy is the energy due to an object's location.
The potential energy of an elevated object equals the work done in raising it.
Kinetic energy is calculated as one-half the mass of an object multiplied by the square of its speed.

Kinetic Energy and Motion

A car traveling at 100 km/s will skid four times farther than the same car at 50 km/s.
When an arrow in a bow has 70 joules of potential energy, it will have 70 joules of kinetic energy after being shot, assuming no energy loss.
Energy conversion occurs without net loss or gain, remaining consistent.

Mechanical Energy Relationships

As a pendulum swings, potential and kinetic energy interchange.
When the speed of a car triples, its kinetic energy increases by nine times.
Launching rockets from an airplane decreases the airplane's kinetic energy.

Work Comparison

Lifting a 70 kg sack 2 meters and a 35 kg sack 4 meters requires the same amount of work.
A ball thrown upward and one thrown downward from the same height will both have equal kinetic energy when hitting the ground under ideal conditions (neglecting air resistance).

Momentum and Kinetic Energy

An object in motion possesses kinetic energy and must also have momentum.
If the velocity of a moving object doubles, its momentum doubles as well.

Efficiency and Simple Machines

Ideal simple machines operate on the principle that work input equals work output.
A typical gasoline-powered car engine operates at approximately 30% efficiency.

Comparisons of Kinetic Energy

A small economy car and a large limousine pushed with equal forces and over equal distances will both receive the same amount of kinetic energy.
In a collision of elastic balls, if one exits with double the speed, it would violate the conservation of energy.

Molecular Speed Relations

For molecules of equal kinetic energy, lighter hydrogen molecules have greater speeds than heavier oxygen molecules.

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Test your knowledge of key concepts from Physics Chapter 9 with these flashcards. Each card presents a term or question followed by its definition or answer to help reinforce your understanding of work and energy. Ideal for review and studying key physics principles.