Energy Part I Review

Work is the effort exerted on something that will change its ___________

Energy

What is the formula for kinetic energy?

KE=1/2mv2

The energy that is stored and held in readiness is _____________

Potential Energy

If you push for a half hour or a whole hour against a stationary wall

• A) no work on the wall is done in either case.• B) half as much work is done during the half

hour.• C) twice as much work is done during the half

hour.• D) it is impossible to determine how much work

is done.

If you push for a half hour or a whole hour against a stationary wall

• A) no work on the wall is done in either case.• B) half as much work is done during the half

hour.• C) twice as much work is done during the half

hour.• D) it is impossible to determine how much work

is done.

• If you push an object twice as far while applying the same force, you do

• A) twice as much work.• B) four times as much work.• C) the same amount of work.• D) half as much work.

• If you push an object twice as far while applying the same force, you do

• A) twice as much work.• B) four times as much work.• C) the same amount of work.• D) half as much work.

• If you find that twice as much work is needed to perform a task but it takes twice as much time, the amount of power required is

• A) twice as much.• B) four times as much.• C) sixteen times as much.• D) unchanged.

• If you find that twice as much work is needed to perform a task but it takes twice as much time, the amount of power required is

• A) twice as much.• B) four times as much.• C) sixteen times as much.• D) unchanged.

If you lift a load of gravel twice as high, what happens to work?

Work doubles!

When you lift a load of gravel against Earth’s gravity, ______________ is done

Gravity

If you lift a load of gravel twice as heavy, what happens to work?

Work doubles!

Why does work double?

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

• A) energy.• B) power.• C) effort.• D) none of these

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

• A) energy.• B) power.• C) effort.• D) none of these

What would be the actual formula for

work = kinetic energy

Fd=1/2mv2

Draw a pendulum where the position is at ½ max PE and

½ max KE

What does the kinetic energy of an object depend on?

The mass of the object and its speed

• If you do work on an object in one-third the usual time, your power output is

• A) one third the usual power output.• B) the usual power output.• C) three times the usual power output.• D) impossible to predict without additional

information.

• ) If you do work on an object in one-third the usual time, your power output is

• A) one third the usual power output.• B) the usual power output.• C) three times the usual power output.• D) impossible to predict without additional

information.

Rows of wind powered generators are used in various windy locations to generate electric power. The locations behind the wind generators are less

windy than if the generators weren’t there. Why is this?

Conservation of energy – that energy is transferred to the mechanical

energy of the turbine

• The power required to exert 1 N force, over a distance of 1 m in 1 second is

• A) 1 W.• B) 2 W.• C) 1/3 W.• D) 3 W.• E) none of these

• The power required to exert 1 N force, over a distance of 1 m in 1 second is

• A) 1 W.• B) 2 W.• C) 1/3 W.• D) 3 W.• E) none of these

What is thermonuclear fusion?

The fusion of nuclei of hydrogen atoms together to form helium

What type of energy does thermonuclear fusion release?

Radiant energy

Does a weightlifter lifting a barbell overhead do work? Why/Why not?

Yes! Force and distance!

• Do 100 J of work in 50 s and your power output is

• A) 1/2 W• B) 2 W.• C) 4 W.• D) 50 W.• E) 5,000 W.

• Do 100 J of work in 50 s and your power output is

• A) 1/2 W• B) 2 W.• C) 4 W.• D) 50 W.• E) 5,000 W.

Work falls into 2 categories, what are these?

1)Work done against another force

2)work done to change the speed of an object

Give 2 examples of potential energy stored in chemical form

Food, fuel, batteries

What is the unit of measure for work? (most used)

Joule

A Joule is what 2 units multiplied?

Newtons Meters

• If an object is raised twice as high, its potential energy will be

• A) half as much• B) twice as much.• C) four times as much.• D) impossible to determine unless the time is

given.

• If an object is raised twice as high, its potential energy will be

• A) half as much• B) twice as much.• C) four times as much.• D) impossible to determine unless the time is

given.

• An object lifted 10 meters gains 200 J of potential energy. If the same object is lifted 20 meters, its potential energy gain is

• A) half as much.• B) the same.• C) twice as much.• D) four times as much.• E) more than four times as much.

• An object lifted 10 meters gains 200 J of potential energy. If the same object is lifted 20 meters, its potential energy gain is

• A) half as much.• B) the same.• C) twice as much.• D) four times as much.• E) more than four times as much.

• An object that has kinetic energy must be• A) moving.• B) falling.• C) at an elevated position.• D) at rest.• E) none of these

• An object that has kinetic energy must be• A) moving.• B) falling.• C) at an elevated position.• D) at rest.• E) none of these

How much work is needed to lift a bag of groceries that weights

300N to a height of 3m?

900J

What is the definition of power?

How fast work is done

Energy is neither created nor destroyed only

_____________

Transferred

Potential energy, gravitational or otherwise, has significance only

when it _____________

Changes

• An object may have potential energy because of its

• A) speed.• B) acceleration.• C) momentum.• D) location.• E) none of these

• An object may have potential energy because of its

• A) speed.• B) acceleration.• C) momentum.• D) location.• E) none of these

What is the formula for potential energy?

PE=mgh

What is the definition of power?

Power = work done / time interval

The potential energy due to elevated positions is called __________________________

Gravitational Potential Energy

What is the formula for the work-energy theorem?

Work = DELTA KE

• When bullets are fired from an airplane in the forward direction, the momentum of the airplane will be

• A) decreased.• B) unchanged.• C) increased.

• When bullets are fired from an airplane in the forward direction, the momentum of the airplane will be

• A) decreased.• B) unchanged.• C) increased.

• A clerk can lift containers a vertical distance of 1 meter or can roll them up a 2 meter-long ramp to the same elevation. With the ramp, the applied force required is about

• A) half as much.• B) twice as much.• C) the same.• D) four times as much.

• A clerk can lift containers a vertical distance of 1 meter or can roll them up a 2 meter-long ramp to the same elevation. With the ramp, the applied force required is about

• A) half as much.• B) twice as much.• C) the same.• D) four times as much.

When you are driving at 90km/h how much more distance do you need to stop compared with driving at 30km/h

9 times as much work so 9 times as much distance

A liter of fuel can do a certain amount of work, but the power produced when we burn it can be any amount depending on how _________ it

burned.

Fast

If a forklift is replaced with a new forklift that has twice the power, how much more dirt can it lift in the same amount of time? If it lifts

the same dirt, how much faster can it operate?

Forklift that delivers 2x the power will lift 2x the load in the same timeOr same load in half the time

A car moving twice the speed of another takes ________ times as much work to stop.

4x

What does the Law of Conservation of Energy state?

Energy cannot be created or destroyed; it may be transformed

from one form into another, but the total amount of energy never

changes

What must an object be doing in order to have kinetic energy?

Moving

Energy from the Sun is released in the form of radiant energy and is transferred in plants to what type of energy?

Chemical energy

What is the circus diver’s PE at point A?

A. 5,000 J

Can an object have energy?

Yes, PE !

• A bow is drawn so that it has 40 J of potential energy. When fired, the arrow will ideally have a kinetic energy that is

• A) less than 40 J.• B) more than 40 J.• C) 40 J.• D) impossible to predict without additional

information

• A bow is drawn so that it has 40 J of potential energy. When fired, the arrow will ideally have a kinetic energy that is

• A) less than 40 J.• B) more than 40 J.• C) 40 J.• D) impossible to predict without additional

information

The amount of friction that the road supplies to a skidding tire is ______________if the car moves more quickly.

Same

What are the two most common forms of mechanical energy?

Energy due to the position of something (PE) or the movement of

something (KE)

• When an automobile is braked to a stop, its kinetic energy is transformed to

• A) stopping energy.• B) potential energy.• C) energy of motion.• D) energy of rest.• E) heat.

• When an automobile is braked to a stop, its kinetic energy is transformed to

• A) stopping energy.• B) potential energy.• C) energy of motion.• D) energy of rest.• E) heat.

An automobile going 100km/h with 4 times the kinetic energy that it would have at 50km.h skids __________ times as far

4x