U7 concepts

Consider the three situations described below. In which situation(s) would the mechanical energy NOT be conserved?

A mountain climber slowly but steadily ascends a steep cliff, A car skids to a stop across a level highway.

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

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

Which of the following variations will increase the kinetic energy of an object?

Increase the object's mass, Increase the object's speed.

The standard metric unit of work is the ____

Joule

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

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

a rate quantity and work is not a rate quantity

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

at rest above the ground ( a non-zero height), moving above the ground ( a non-zero height)

Suppose that an object moves downward with a decreasing speed. In this situation, the object's kinetic energy would ______, its potential energy would ______, and its total mechanical energy would _____

decrease, decrease, decrease

Suppose that an object slows down while moving horizontally. In this situation, the object's kinetic energy would _______, its potential energy would ______, and its total mechanical energy would _____

decrease, remain the same, decrease

If an object has potential energy, then its kinetic energy is 0 J.

false

if an object is moving above the ground (at a non-zero height), then it will not have any potential energy

false

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

force acting upon the object, displacement

Some forces are categorized as conservative forces (or internal forces) while others are categorized as non-conservative forces (or external forces). Which of the following forces are generally categorized as non-conservative (or external) forces?

force of friction, air resistance force, tension force, applied force, normal force

Which of the following variations will increase the potential energy of an object?

increase the object's height, increase the object's mass

Suppose that an object moves upward with an increasing speed. In this situation, the object's kinetic energy would _______, its potential energy would ______, and its total mechanical energy would _____

increase, increase, increase

Suppose that an object speeds up while moving horizontally. In this situation, the object's kinetic energy would ______, its potential energy would ______, and its total mechanical energy would ____

increase, remain the same, increase

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

An object will have kinetic energy if it is _____.

moving, moving on the ground (height = 0 m), moving above the ground (a non-zero height)

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

In order for an object to conserve its total mechanical energy it is absolutely necessary that ____

non-conservative (i.e., external) forces do NOT do net work upon the object

An object's mechanical energy will NOT be conserved if ____

non-conservative forces (i.e., external forces) are doing work upon the object

Two objects of identical mass begin from rest at the same height at the top of two different hills - hill A and hill B. The hills are inclined at two different angles (see diagram). The objects are released from rest and slide to the bottom; resistance forces can be considered to be negligible. The object on top of hill ____ will have the greatest speed at the bottom of the incline.

nonsense! both objects will have identical speeds at the bottom

If the only forces doing work upon an object are conservative (or internal) forces, then the total mechanical energy of the object will _____. If the only forces doing work upon an object are conservative (or internal) forces, then the total mechanical energy of the object will _____.

not change, change - either increase or decrease

If the only forces doing work upon an object are conservative (or internal) forces, then the total mechanical energy of the object will ______. If only forces doing work upon an object are non-conservative (or external) forces, then the total mechanical energy of the object will _____

not change, change - either increase or decrease

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

Suppose that an object moves downward at a constant speed. In this situation, the object's kinetic energy would _____, its potential energy would ______, and its total mechanical energy would _____

remain the same, decrease, decrease

Suppose that an object moves upward at a constant speed. In this situation, the object's kinetic energy would ______, its potential energy would ______, and its total mechanical energy would _____

remain the same, increase, increase

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

scalar, magnitude alone

Some forces are categorized as conservative forces (or internal forces) while others are categorized as non-conservative forces (or external forces). Which of the following forces are generally categorized as conservative (or internal) forces?

spring force, force of gravity

Power is defined as _____

the rate at which work is done upon an object

The total mechanical energy of an object is ____

the sum of its kinetic energy and its potential energy

If the total mechanical energy of an object is conserved, then ____

the sum of the KE and the PE is the same for the initial state as it is for the final state

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

the sum of the kinetic energy and the potential energy is changing, mechanical energy is being converted into non-mechanical forms (or vice versa)

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

If non-conservative forces (i.e., external forces) are acting upon an object, then the total mechanical energy of that object could still remain constant.

true

The standard metric unit of power is a _____

watt

If both conservative (i.e., internal) and non-conservative (i.e., external) forces are doing net work upon an object, then the total mechanical energy of the object ____.

will definitely change

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