Unit 5 Review

Question 1

What is work?

Answer 1

force applied through a distance.

Question 2

What two elements are required for work to be done?

Answer 2

1. the applied force must make the object move
2. the movement must be in the same direction as the applied force

Question 3

True or False: If you push against a desk and nothing moves, you have done work.

Answer 3

False

Question 4

Fill in the blank: Work requires both _______ and motion.

Answer 4

force

Question 5

What is the formula for calculating work?

Answer 5

W = Fd

work (in joules) = applied force (in newtons) x distance (in meters)

W = Fd

Question 6

True or false: Both work and energy are measured in joules.

Answer 6

True

Question 7

During the ascent phase of a rep of the bench press, the lifter exerts an average vertical force of 1000N against a barbell while the barbell moves 0.8 m upward. 

How much work did the lifter do to the barbell?

Answer 7

800 J

Question 8

The rate at which energy is transferred is also known as what?

Answer 8

power

Question 9

How do you calculate power?

Answer 9

you divide the amount of work done by the time it takes to do that work

P = W / t

Question 10

What unit is power measured in?

Answer 10

watts

Question 11

True or false: One watt is equal to one joule per second.

Answer 11

True

This means that joules per second and watts can be used interchangeably.

Question 12

Provide the definition of machine.

Answer 12

a device that changes the force or increases the motion from work

Window blinds are a machine that changes the direction of an input force

Question 13

A simple machine is a machine that does work with only ____ movement of the machine.

Answer 13

one

Question 14

List the six types of simple machines.

Answer 14

1. Lever
2. Pulley
3. Wheel and axle
4. Inclined plane
5. Screw
6. Wedge

Question 15

True or false: The pulley and the wheel and axle are modified levers.

Answer 15

True

Question 16

What two simple machines are modified inclined planes?

Answer 16

1. Screw
2. Wedge

Question 17

Provide the definition of efficiency.

Answer 17

a measure of how much of the work put into a machine is changed into useful output work by the machine

Simplified: how much input work is changed to output work

Question 18

True or false: Some machines are 100% efficient.

Answer 18

False

Question 19

True or false: Ideal machines₁ are impossible to build.

₁ | A machine that has 100% mechanical efficiency

Answer 19

True

Question 20

Why are ideal machines impossible to build?

Answer 20

Every machine has moving parts, and some use input work to overcome friction

Question 21

Provide the equation for efficiency.

Answer 21

e = W_out / W_in * 100

Efficiency is usually expressed as a percentage

Question 22

List one way that machines can be made more efficient.

Answer 22

adding a lubricant

Some examples of lubricants are oil and grease.

Question 23

List the two forces involved when a machine is used to do work.

Answer 23

1. F_in
2. F_out

F_in - stands for the effort force
F_out - the force applied by the machine

Question 24

The ratio of the output force to the input force is also known as what?

Answer 24

mechanical advantage

MA = F_out / F_in

Question 25

True or false: Every change that occurs involves energy.

Answer 25

True

Question 26

The ability to do work is also known as ______.

Answer 26

energy

Question 27

Provide the definition of a system.

Answer 27

Anything that you can imagine a boundary around. ## Footnote A system can be a single object, such as a baseball, or a group of objects, such as the solar system.

Question 28

Provide the six different forms of energy.

Answer 28

1. Electrical 2. Chemical 3. Radiant (light) 4. Thermal 5. Nuclear 6. Sound ## Footnote Any form of energy can be converted to another.

Question 29

The energy a moving object has because of its motion is also known as ...

Answer 29

kinetic energy.

Question 30

The kinetic energy of a moving object depends on the object's _____ and its ________.

Answer 30

mass, velocity (speed)

Question 31

Provide the kinetic energy equation.

Answer 31

KE = 1/2 mv²

Question 32

Provide the definition of potential energy.

Answer 32

the stored energy of position possessed by an object due to the interactions between another object ## Footnote Ex.) **Gravitational Potential Energy** - An object at a height relative to the Earth has potential energy because of the gravitational pull between the object and the Earth. The higher the object, the more energy it has stored.

Question 33

Provide the definition of chemical potential energy.

Answer 33

Energy stored due to chemical bonds

Question 34

Gasoline, food, and some other substances all have what in common?

Answer 34

They all have chemical potential energy

Question 35

Chemical potential energy is stored due to the bonds that hold the ______ together and is released when the _____ is burned.

Answer 35

atoms, gas ## Footnote Explanation: In food, your body breaks the bonds in the molecules and uses the released energy to power you. Think of it like a battery--it stores energy that can be released when you "use it" (break bonds).

Question 36

What is going on below?

Answer 36

chemical potential energy is released

Question 37

Energy due to the gravitational forces between objects is also known as what?

Answer 37

Gravitational Potential Energy (GPE)

Question 38

Provide the equation to calculate GPE.

Answer 38

GPE = mgh ## Footnote **gravitational potential energy** (J) = **mass** (kg) x **gravity** (N/kg) x **height** (m)

Question 39

All forms of energy can be measured in ________.

Answer 39

joules

Question 40

What does the law of conservation of energy state?

Answer 40

energy cannot be created nor destroyed

Question 41

True or false: The total amount of energy in the universe is changing.

Answer 41

False ## Footnote The law of conservation of energy states that energy never can be created or destroyed, therefore the total amount of energy in the universe is constant.

Question 42

When energy conversion takes place, does the total amount of energy change?

Answer 42

no

Question 43

Mechanical energy is the sum of the _________ and _________ energies of objects in a system.

Answer 43

kinetic, potential

Question 44

True or false: The mechanical energy of a system remains constant or nearly constant.

Answer 44

True ## Footnote This happens because as potential energy decreases, kinetic energy increases, and vice versa.

Question 45

If you were swinging or riding a rollercoaster, the potential energy is at its greatest at the ___ of your path.

Answer 45

top

Question 46

If energy is conserved, why does kinetic energy not stay constant so that you could bike, swing, or rollerblade forever?

Answer 46

Friction and air resistance cause some of the mechanical energy to change to other forms of energy.

Question 47

Fuel stores ________ potential energy.

Answer 47

chemical ## Footnote The engine transforms the chemical potential energy of gasoline molecules into the kinetic energy of a moving car or bus.

Question 48

``` A construction worker is lifting a load of bricks onto a truck. He does 200 J of work in 40 seconds. ``` What is his power output?

Answer 48

5 watts (W)

Question 49

In which situation is a person doing work on an object? **A.** A man exerts 350 N force on a rope attached to a house. **B.** A worker holds a box 1 m off the floor. **C.** A school crossing guard raises a stop sign that weighs 10 N. **D.** A student walks while wearing a backpack that weighs 15 N.

Answer 49

C. A school crossing guard raises a stop sign that weighs 10 N. ## Footnote Work is only done when a force is applied, and it causes an object to move in the direction of the force.

Question 50

A roller coaster is at the top of a 72 m hill and weighs 134 kg. The coaster has _________ energy. Calculate it.

Answer 50

* potential * 94,550.4 J