SAU Conceptual Physics Dynamic Study Module CH.7

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A weightlifter exerts an upward force on a 1000-N barbell and lifts the barbell 1 meter upward in 2 seconds. Approximately how much power does the weightlifter exert on the barbell during this time?

500 watts

Which of the following machines would be categorized as simple machines?

Levers & pulleys

Which of the following increases when a person runs a bag of groceries up the stairs rather than walking it up?

Power

Which of the following are major sources of energy?

Sun, wind, fossil fuels, and hydroelectric

When helping a friend move into a new home, you push a chair across the room. What do you know about the force of gravity applied to the chair?

The force of gravity applied to the chair does not change the energy of the system (the chair) and therefore does no work on the system.

When helping a friend move into a new home, you push a chair across the room. What do you know about the force that you exert on the chair?

The force you exert on the chair contributes to the overall change in kinetic energy of the system (the chair) with a positive amount and therefore does positive work on the system.

When helping a friend move into a new home, you push a chair across the room. What do you know about the force of friction applied to the chair by the floor?

The frictional force applied to the chair contributes to the overall change in kinetic energy of the system (the chair) with a negative amount and therefore does negative work on the system.

A block slides along a rough surface and comes to a stop. What can you conclude about the frictional force exerted on the block?

The frictional force does negative work on the block and decreases its kinetic energy.

When you lift a book upward off of a table, what is true about the work done on the book by the force of gravity?

The work done by the force of gravity is negative and proportional to the upward displacement of the book.

In which of these processes is the total energy of the system conserved?

Two balls of putty (the system) collide in midair and stick together.

A variety of forces are applied to an object such that the net force does positive work on that object. What can you conclude about the speed of the object?

When the total work done on the object is positive, the object's speed will increase.

__________ is required to change an object's energy.

Work

A simple machine that has a larger output force than input force must have

a larger input distance than output distance

kinetic energy is best defined as

energy of motion

Both __________ and __________ are required to change an object's energy level.

force, distance

The law of conservation of energy

is always true

Which of the following can create or destroy energy?

nothing

The most concentrated source of usable energy is that stored in

nuclear fuels

If Quantity X is conserved for a certain system and during a certain process, that means

quantity X for that system does not change in any way during that process

Potential energy is best defined as

stored energy

The change in the amount of work is equal to the change in kinetic energy is defined in

the work-energy theorem

It is impossible to achieve 100 percent efficiency in an engine due to

thermal energy

An apple falls from a tree. On the way to the ground, the apple's

total energy remains constant, potential energy decreases, and kinetic energy increases

Work done by a spring is work done by a

variable force

A man pushes against a wall with 200 N of force. The amount of work he does to the wall is

zero


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