Physics Quiz: Work/Energy/Power

work

a force acting upon an object to cause a displacement is known as

joule and newton*meter

two acceptable units for work are .

the rate at which work

power is defined as ______ is done

they both do the same thing (same work), but can have different rates (power) by having less time than the other

although two elevators do identical jobs, they could each have different power outputs. Why?

watts and joule/second

units for power are

mgh

GPE =

GPE

= mgh

work/time or displacement of energy/time

power =

power

work/time or displacement of energy/time =

Gravitational potential energy

GPE

Kinetic energy

KE

1/2mv^2

KE =

KE

1/2mv^2 =

elastic potential energy

EPE

1/2kx^2

EPE =

EPE

1/2kx^2 =

Etoti = Etotf

Energy conservation equation

work

force acting over some amount of distance

impulse

force acting over some amount of time to cause a change in momentum

No, force does not cause displacement

A teacher applies force to a wall and becomes exhausted — is there work done?

Yes, force is applied and causes displacement

A weightlifter lifts a barbell above her head. Is work done?

No, upward force is applied, but there is no horizontal displacement

A waiter carries a tray full of meals across a dining room at a

constant speed. Is there work being done?

Yes, force is applied an there is displacement

A rolling marble hits a note card and moves it across a table. Is work done?

It is a scalar quantity, meaning it only has magnitude and no direction.

Is work scalar or vector?

Adding or removing energy from the object

what does the + or - sign on a work value indicate

negative (-)

An eastward-moving car skids to a stop across dry pavement. Is this negative or positive work?

Positive (+)

A freshman stands on his toes and lifts a World Civilization book to the top shelf of his locker. Is this negative or positive work?

Positive (+)

At Great America, a roller coaster car is lifted to the peak of the first hill on the Shock Wave. Is this negative or positive work?

Negative (-)

A falling parachutist opens the chute and slows down. Is this negative or positive work?

Negative (-)

A catcher puts out his mitt and catches the baseball. Is this negative or positive work?

Perpendicular directions

What direction is force and displacement when there is no work being done?

opposite

What direction is force and displacement when there is negative work being done?

same direction

What direction is force and displacement when there is positive work being done?