work, energy, and power

Question 1

work

Answer 1

work is the force multiplied by the distance moved in the direction of the force

Question 2

work formula

Answer 2

W = Fs

Question 3

unit of work

Answer 3

Joule / Newton Metre

J / Nm

Question 4

joule

Answer 4

the work done when a force of 1 newton moves its point of application 1 metre in the direction of the force

Question 5

energy

Answer 5

the ability to do work or move something

Question 6

unit of energy

Answer 6

joule

Question 7

types of energy

Answer 7

stored energy

action energy

Question 8

stored energy

Answer 8

potential
nuclear
chemical

Question 9

action energy

Answer 9

kinetic
heat
light
sound
electrical

Question 10

potential energy

Answer 10

the energy an object has due to its position or shape

Question 11

potential energy formula

Answer 11

(Eₚ) = mgh

Question 12

Nuclear energy

Answer 12

the nucleus at the centre of an atom has an enormous supply of stored energy

Question 13

chemical energy

Answer 13

the stored energy in food, fuel, and a battery

Question 14

kinetic energy

Answer 14

the energy associated w/ moving objects

Question 15

kinetic energy formula

Answer 15

(Eₖ) = 1/2mv²

Question 16

Pendulum - kinetic and potential energy

Answer 16

• When a pendulum is at its highest point, the potential energy is at maximum, the kinetic energy is zero
• As it swings, it changed completely to kinetic and back to potential

Question 17

heat energy

Answer 17

energy possessed by an object due to the kinetic energy of its atoms or molecules

the hotter something is, the more it moves around

Question 18

light energy

Answer 18

Light energy is a form of electromagnetic radiation

provides the energy for plants to grow + make food and oxygen
photosynthesis

Question 19

sound energy

Answer 19

sound energy makes things vibrate

Question 20

electrical energy

Answer 20

this energy comes from moving charges

Question 21

magnetic energy

Answer 21

the ability to attract or repel other substances

Question 22

mass

Answer 22

mass is a form of energy

E = mc²

Question 23

principle of conservation of energy

Answer 23

states energy can neither be created nor destroyed; it can merely change from one form to another

Question 24

power

Answer 24

the amount of work done per second

• As work is done, energy is changed from one form to another
• So power is the rate at which energy is converted from one form to another

Question 25

power formula

Answer 25

power = work done/time taken

Question 26

watts and joules

Answer 26

1 watt = 1 joule s⁻¹

Question 27

efficiency

Answer 27

the efficiency of a machine is a measure of how good it is at converting energy without waste

Question 28

efficiency formula

Answer 28

power output/power input x 100 = %

Question 29

friction

Answer 29

a force that opposes relative motion between two bodies in contact
-friction always opposes motion

Question 30

lubricants

Answer 30

substances that reduce friction

Question 31

equilibrium

Answer 31

• static equilibrium

- dynamic equilibrium

Question 32

static equilibrium

Answer 32

when an object is not moving is in equilibrium

eg. a metre stick

Question 33

dynamic equilibrium

Answer 33

eg. a moving card which balances the forces of the engine and friction on the tyres

Question 34

viscocity

Answer 34

the resistance to flow in a fluid

Question 35

sphere falling thru a fluid

Answer 35

• has 3 forces acting on it
• its weight W acting downwards, as upthrust U due to displaced fluid, (Archimedes’ Principle). and a friction force F acting upwards
• U and W are constant, F increases with velocity

Question 36

loss of kinetic energy in collisions

Answer 36

when two objects collide, momentum is always conserved, provided no external forces act. Usually kinetic energy is not conserved. The lost kinetic energy is converted into other forms such as heat energy and sound energy

Question 37

renewable source of energy

Answer 37

a source of energy that does not get used up

Question 38

eg of renewable energy

Answer 38

wind energy
solar energy
hydroelectric energy
wave energy
biomass energy

Question 39

non renewable energy

Answer 39

oil
coal
peat
natural gas

Question 40

efficient use of energy in the home

Answer 40

insulating walls, attics, floors
double glazing in windows
draught-proofing doors + windows
energy efficient miniature fluorescent bulbs

Question 41

fluorescent bulbs

Answer 41

use less energy than a conventional filament bulb to produce same amount of life

most energy converted to light, not heat

Question 42

power equation

Answer 42

p =w/t

note: w is E, both measured in joules
so you can write it as E = pt as well

Question 43

calculate energy from sun falling on football pitch of dimensions 106mx68m in 90 mins

Answer 43

-turn 90 mins to seconds, then find area of field
-solar constant is 1.36 kW m⁻². This is the energy per
unit area from the sun
-multiply this by the area of the field and the time taken to get answer

energy = solar constant x area x time

Question 44

why its not possible to extract all the energy in the wind striking a wind turbine blade

Answer 44

-wind is slowed down rather than stopped

Question 45

on bouncing from the ground a ball loses 6 joules of energy. What happens to the energy lost by the ball?

Answer 45

-changes into sound/heat/other forms

Question 46

efficiency of a 60W filament lamp that provides 8J of light energy every sec

Answer 46

E = 8/60 x 100

= 13.33%

Question 47

heat generated formula (not in log table)

Answer 47

Power x Time

(bc power is energy per sec,

Question 48

estimating pd using gold leaf electroscope

Answer 48

when cap connected to one point and metal case to another, size of divergence of leaf is measure of pd between the two points

Question 49

work vs power units

Answer 49

work: joules
power: watts

Question 50

momentum unit

Answer 50

kg m s⁻¹ / N(?)