physics unit 6: mops

In order to have work done upon an object, there must be a(n) ____ to cause a(n) ____.

force acting upon the object, displacement

A 5-Newton friction force acts upon a 2-kg object to slow it down as it moves it across a horizontal surface over a distance of 4 meters.  The free-body diagram is shown below.  Which of the following forces are doing work upon the object - either positive or negative?

friction force

A 5-Newton force is applied to a 2-kg object to move it across a horizontal surface at a constant speed for a distance of 4 meters.  The free-body diagram is shown below.  Which of the following forces are doing work upon the object - either positive or negative? 

friction force, applied force

Which of the following are examples of work being done (either positive or negative) upon an object? 

(any options where there is DISPLACEMENT- the answer to this question is all of the answers EXCEPT the one where you’re holding something so it stays at rest and holding something so it stays motionless in the air)

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

A man is walking through an airport with a suitcase.  The man exerts a constant upward force upon the suitcase as he walks a distance of 20 meters.  In this example, the man is doing ____ work upon the suitcase.

zero

A softball player is sliding into third base.  Once 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.

negative

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

scalar; magnitude alone

The essential difference between work and power is that power is _____.

a rate quantity and work is not a rate quantity

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

Power is defined as _____.

the rate at which work is done upon an object

An object will have kinetic energy if it is _____. 

(anything that mentions moving)

An object will definitely have potential energy if it is _____. 

(anything talking about being above the ground)

Consider the types of forces present in the following physical situation:

A dart is traveling through the air towards a dart board.  Assume that air resistance is negligible.

In this situation, the total mechanical energy of the dart ____.

will remain constant

Consider the types of forces present in the following physical situation:

A roller coaster car is coasting down the first drop of the track.  Assume that resistance forces have no effect on the car's motion.

In this situation, the total mechanical energy of the roller coaster ____.

will remain constant

BAR GRAPHS spring loaded dart gun

NO initial kinetic energy; NO work

BAR GRAPHS sledder

NO initial potential energy; NO final kinetic energy; choose choice with only ONE negative work cube, FULL initial kinetic energy, and THREE potential energy

BAR GRAPHS roller coaster with negligible friction/air resistance

NO work, NO initial kinetic energy, NO final potential energy

BAR GRAPHS roller coaster with friction/air resistance

FULL initial potential energy; NEGATIVE work; HALF final kinetic energy

BAR GRAPHS physics cart

HALF initial kinetic energy; FULL work; HALF final kinetic energy; FULL final potential energy

Consider the work energy bar charts shown below.  Select any bar charts that portray a situation in which mechanical energy is NOT conserved. 

any with work

When an object's total mechanical energy is NOT conserved, ____. 

the sum of the kinetic energy and the potential energy is changing

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mechanical energy is being converted into non-mechanical forms (or vice versa)