Work and Energy

Question 1

Describe the concept of work.

Answer 1

it is the process by which energy is transferred from one system to another

Question 2

Describe Kinetic Energy

Answer 2

Energy of motion

Question 3

Write the units for joule.

Answer 3

Question 4

Write the equation for kinetic energy.

Answer 4

Question 5

Gravitational potential energy

Answer 5

U= mgh where m is the mass, g is the gravitational constant, and h is the height

Question 6

Elastic potential energy

Answer 6

Released to spring constant, k (a measure of the stiffness of the spring) and the degree of stretch or compression of a spring squared.

Question 7

Electrical potenial energy

Answer 7

Energy presents in objects in which positively and negativley charged particals are separated

Question 8

Chemical potential energy

Answer 8

The energy stored in the bonds of compounds

Question 9

Total mechanical energy

Answer 9

The sum of kinetic and potential energies in a system.
E = U + K

Question 10

Work done by a system

Answer 10

POSITIVE

Question 11

Work done on a system

Answer 11

NEGATIVE

Question 12

Describe an isovolumetric process.

Answer 12

If volume stays constant as pressure changes then no work is done because there is no area to calculate on the P-V Curve

Question 13

Describe an isobaric process.

Answer 13

pressure remains constant, work can be calculated

Question 14

Explain Power.

Answer 14

The rate at which work is done or energy is transferred.

Question 15

What is the SI unit for Power?

Answer 15

The SI unit for power is watt (W)

Question 16

Write the equation for power.

Answer 16

Question 17

Work-Energy Theorem

Answer 17

States that when work is done on or by a system. the system’s kinetic energy will change by the same amount. In more general applications, the work done on or by a system can be transferred to other forms of energy as well.

Question 18

Mechanical Advantage

Answer 18

The factor by which a simple machine multiplies the input force to accomplish work.

Question 19

The six simple machines

Answer 19

1) Inclined plane
2) Wedge
3) Wheel and axle
4) Lever
5) pulley
6) screw

Question 20

What is the benefit of mechanical advantage?

Answer 20

It allows you more easily accomplish a given amount of work because the input force necessary to accomplish the work is reduced.

Question 21

What is Load?

Answer 21

The output of force of a simple machine, which acts over a given load distance to determine the work output of the simple machine.

Question 22

What is Effort?

Answer 22

The input force of a simple machine, which acts over an effort distance to determine the work input of the simple machine

Question 23

to lift an object to a certain height in the air, one must pull through a length of rope equal to

Answer 23

twice that displacement (but half the force needed)

Question 24

Efficiency

Answer 24

The ratio of the machines work output to the work input when nonconservative forces are taken into account.

Question 25

6 pulleys, effort is now ______ total load

Answer 25

1/6 total load (6 times amount of rope, efficiency will decrease due to weight of pulleys and friction)

Question 26

Uniform circular motion

Answer 26

no work is done because the displacement vector and the force vector are always perpendicular
potential energy is constant

Question 27

At terminal velocity

Answer 27

the force of gravity and air resistance are equal, leading to translational equilibrium

Question 28

What are the 2 criteria for Ek?

Answer 28

you must have mass and you must be moving

Question 29

Kinetic energy’s relation to speed/velocity

Answer 29

related to SPEED, not VELOCITY (direction does not matter); and its related to speed squared (make sure to know the relative increases type logic; if speed doubles, Ek quadruples)

Question 30

Dynamic Pressure

Answer 30

the kinetic energy of a flowing liquid; this is a term in Bernoulli’s Equation

Question 31

Gravitational Potential Energy

Answer 31

energy relative to object’s position to the datum (0 Eg; ground level)

Question 32

Gravitational Potential Energy Equation

Answer 32

Eg = mgh

Question 33

k in the Ee equation

Answer 33

spring constant; measures stiffness of elastic/spring

Question 34

If an object experiences friction, where is that kinetic energy lost?

Answer 34

as heat

Question 35

2 most common MCAT conservative forces

Answer 35

gravitational and electrostatic; do not lose energy from a system, but convert it to potential

Question 36

How do you determine if a force is conservative?

Answer 36

1) if it takes a round trip path (back to same starting position) and ΔE is 0, or 2) if ΔE is equal for taking ANY path between 2 points… = the force is conservative; it takes energy from 1 form and gives it back as another, E total remains the same, no loss to non-conservative force!

Question 37

Conservation of Mechanical Energy Equation

Answer 37

ΔE = ΔEp + ΔEk = 0

Question 38

2 ways to transfer energy

Answer 38

work and heat ONLY!!!!!!!!!!!

Question 39

In work, what component of force actually does work?

Answer 39

the component PARALLEL (antiparallel) TO THE DISPLACEMENT VECTOR

Question 40

What happens when gas pushes up on a piston?

Answer 40

it does work to move it up, volume increases

Question 41

What happens when a piston pushes down on a gas?

Answer 41

it does work on the gas, compressing it

Question 42

What sign is work DONE BY THE SYSTEM? What does this mean?

Answer 42

positive (+); means the system (gas) has expanded

Question 43

What sign is work DONE ON THE SYSTEM? What does this mean?

Answer 43

negative (-); means the system (gas) was compressed

Question 44

If ΔV = 0 for a gas system, how much work has been done?

Answer 44

0 J! no work; there is no area to calculate under a P-V curve; isovolumetric/isochoric process

Question 45

f ΔP = 0 for a gas system, how much work has been done?

Answer 45

W = PΔV joules of work; on a P-V graph, this makes a rectangle; Isobaric Process