work work

Question 1

what is work?

Answer 1

W = Fd (d = delta x)
W = force * displacement

the result of a force MOVING an object

Question 2

does work also work independnetly on axes?

Answer 2

yaen

Question 3

what is the joule the unit of?

Answer 3

work AND energy, units of N*m

Question 4

what happens when the angle is 90 degrees or opposite to the displacement?

Answer 4

W = fdcos(theta)

at 90 degrees cos = 0, independent entirely

at 0 degrees cos = 1, simple Force*d

at 180 degrees energy is being taken away, work is negative, cos(180) = -1 thus -F*d

Question 5

what do you do when force is changing?

Answer 5

throwback to area method:
area of work*displacement if force is constant

if force is changing, area is still work done, displacement * force/2

Question 6

what is power

Answer 6

the rate at which work is done, or work/time (J/s)

P = W/t = Fdcos(theta)/t

simplify d/t = velocity

Depending on what you have,
P = f*v(cos(theta))

Question 7

unit for power (J/s)

Answer 7

watts

Question 8

ENERGY TYPES

Answer 8

1. Kinetic (energy of movement)
2. potential (energy of position)
3. mechanical (sum of potential and kinetic
4. nonmechanical (thermal, lgiht, sound, chemical, nuclear, etc. (generally microscopic forms of kinetic and/or potential))

Question 9

kinetic energy equation

Answer 9

K = 1/2mv^2

Question 9

stored/potential energy equation

Answer 9

U = mg(delta h)
usually given letter U for some reason

Question 10

units of KE

Answer 10

kg * m^2/s^2 (joules)

Question 11

units of PE

Answer 11

kg * m/s^2 * m (joules)

Question 12

conservation of MECHANICAL energy and conservative vs. nonconservative forces

Answer 12

conservative forces conserve mechanical energy (i.e. gravity, magnetism, nuclear forces, force of a sprint) energy only changes form

nonconservative - mechanical energy —>nonmechanical, ex. rubbing hands causes heat

Question 12

if i throw the tennis ball straight upwards at 5.0 m/s how high will it go?

Answer 12

positionf = peak of throw

Ki + Ui = Kf + Uf

Ui = 0, Kf = 0

therefore Ki = Uf

1/2mv^2 = mgh

mass cancels out

1/2(25) = 10h
h = 1.25

Question 13

can potential energy be directly measured?

Answer 13

no

Question 14

can kinetic energy be directly measured?

Answer 14

yes

Question 15

true/false: object CAN be treated as having no internal structure despite multiple objects inside and transfer of matter/force/energy w/i system

Answer 15

true, though not when trying to calculate internal forces obvi

Question 16

true/false: object’s internal structure cannot transfer force/matter/energy w/i a system due to conservation of mechanical energy

Answer 16

no bro what

Question 17

potential energy only exists in what kind of system?

Answer 17

multiple object systems like a boy jumping and the earth pulling it down, relationship between earth and boy produces potential energy, but by by himself does not have PE

Question 18

kinetic energy only exists in what kind of system?

Answer 18

ones in motion, but a single object can have KE by itself.

Question 19

AP FRQ: A ball rolls from rest down a ramp w/some friction

A. describe what happens to the total mechanical energy of the system consisting of the ball:

B. Describe what happens to the total mechanical energy of the system conssiting of teh ball and earth

Answer 19

A. from the ball’s perspective (PE does not exist) kinetic energy increases as it speeds up

B. Total mechanical energy decreases due to friction transferring to thermal energy

Question 20

what are the most common ways an object loses mechanical energy?

Answer 20

friction (thermal), sound,

Question 21

true/false: energy conservation methods are generally easier/preferable when they can be applied

Answer 21

true

Question 22

energy conservation vs. kinematics (what things can they/can they not calculate?)

Question 23

describe mechanical energy when a hand is accelerating a ball upwards

Answer 23

both kinetic AND potential are increasing,

Question 24

when is ME not conserved?

Answer 24

when there is a non-conservative force like friction/air resistance

when there is ANY external force doing work on the system (force of friction or force applied)

Question 25

Work-energy theorem

Answer 25

change in energy = work

change in KINETIC energy NET WORK done on system

Ki + Ui + W = Kf + Uf
(W = F*x)

Question 26

ME relationship equation (all the added stuff = the other added stuff)

Answer 26

Ki + Ui + W = Kf + Uf

Question 27

what is the work-energy theorem most commonly used for?

Answer 27

finding stopping distance

Question 28

take the equation
W = F * d * cos(theta)

which values are vectors? which are absolute values (not necessarily scalar)?

Answer 28

Force and distance are only used in magnitude, therefore are positive

degrees or theta is also always positive, as the theta here is only the DISTANCE OF ANGLE BETWEEN the force vector and distance axis

Depending on whether cos(theta) turns out to be positive or negative, W will be the same sign