Work, Power, Energy

(positive or negative work) A cable is attached to a bucket and the force of tension is used to pull the bucket out of a well

+

(positive or negative work) A pendulum bob swings from it highest position to its lowest position under the influence of the force of gravity

+

(positive or negative work) In a physics lab, an applied force is exerted parallel to a plane inclined at 30-degrees in order to displace a cart up the incline

+

(positive or negative work) Rusty Nales uses a hammer to exert an applied force upon a stubborn nail to drive it into the wall

+

(positive or negative work) In baseball, the catcher exerts an abrupt applied force upon the ball to stop it in the catcher's mitt

-

(positive or negative work) Near the end of the Shockwave ride, a braking system exerts an applied force upon the coaster car to bring it to a stop

-

(true or false) If an object is moving above the ground (at a non-zero height), then it will not have any kinetic energy.

False

External Forces

Fapp Ffrict Fair Ftens Fnorm

In order to have work done upon an object, there must be ___ to cause ____

Force acting upon the object, displacement

Internal Force

Force of Gravity Spring Force

Work is a _____ quantity; it is fully described by stating its ____

Scalar, magnitude alone

Work

When a force acts upon a object to cause a displacement of the object, work is done upon the object

(work or not work) A book falls off a table and free falls to the ground.

Work

(work or not work) A rocket accelerates through space

Work

Potential energy

the stored energy of position possessed by an object

Student A and Student B are doing two identical tasks involving physical work. Student A does the task in more time than student B. in this physical situation,

the two students do the same amount of work, but student B has the greater power rating

Which of the following examples of work being done - A rightward force is applied to an object to move it to the right at a constant speed - A rightward force is applied to an object to accelerate it to the right - A force is applied to an object to hold it at rest on an inclined plane - An upward force is applied to an object to suspend it motionless in mid-air - An upward force is applied to a downward moving object to slow it down as it moves - An upward force is applied to an object to move it upward at constant speed - An upward force is applied to an object to accelerate it upward

- A rightward force is applied to an object to move it to the right at a constant speed -A rightward force is applied to an object to accelerate it to the right - An upward force is applied to a downward moving object to slow it down as it moves - An upward force is applied to an object to move it upward at constant speed - An upward force is applied to an object to accelerate it upward

Which of the following variations will increase the potential energy of an object? - Decrease the object's height -Decrease the object's mass - Decrease the object's speed - Increase the object's height - Increase the object's mass - Increase the object's speed

- Increase the object's height - Increase the object's mass

Which will increase the kinetic energy of an object? (list all that apply) - Decrease the object's height -Decrease the object's mass - Decrease the object's speed - Increase the object's height - Increase the object's mass - Increase the object's speed

- Increase the object's mass - Increase the object's speed

3 ingredients to work

- force - displacement - cause

An object will definitely have potential energy if its _____. (list all that apply) - moving above the ground - moving on the ground - moving - at rest above the ground - at rest on the ground - at rest

- moving above the ground - at rest above the ground

1 Joule =

1 Newton * 1 meter

In order for a force to qualify as having done work on an object, there must be a displacement and the force must ______ the displacement

CAUSE

The standard metric unit of work is the

Joule

Units of work

Joule (J)

Mac and tosh run up the same hill. Mac has twice the mass as Tosh. Tosh climbs up the hill in one-half the time as Mac. In this situation,

Mac does more work than Tosh, but they have the same power rating.

Kinetic energy is the energy that an object possesses due to its _____ and potential energy is the energy that an object possesses due to its ______

Motion, position

A softball player is sliding into third base. One she hits the dirt, the force of friction acts upon her to slow her down as she slides a distance of 1.5 meters across the distance. In this example, friction is doing ____ work upon the player. - positive - negative - zero

Negative

(work or not work) A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed.

Not work

A child is pushing an empty box across a living room floor. The child exerts a constant rightward force upon the box to move it a distance of 2 meters to the right. In this example the child is doing ____ work upon the box.

Positive

Power equation

Power = Work / time

Work is done when - the displacement is not zero - the displacement is zero - the force and displacement are perpendicular - the force is zero

The displacement is not zero

Work equation

W = F • d • cos Θ

Standard metric unit of power is the

Watt

Kinetic energy

is the energy of motion

Mechanical energy

is the energy that is possessed by an object due to its motion or due to its positio

Total Mechanical Energy

merely the sum of the potential energy and the kinetic energy

(positive or negative work) A busy spider hangs motionless from a silk thread, supported by the tension in the threaf

no work

(work or not work) A teacher applies a force to a wall and becomes exhausted.

not work

Power

rate at which work is done.

Power is defined as

the rate at which work is done upon an object