Work & Energy

Question 1

what is work? unit? formula?

Answer 1

when a force acting on a body displaces it in the direction of force.
joule (J)
W=F x S

Question 2

define joule?

Answer 2

one joule equals to the work done by 1N force that displaces a body through 1m distance.

unit of work and energy

J= N x m

Question 3

what is energy? formula for K.E.

Answer 3

a body possesses energy if it has the ability to do work.

Question 4

what is kinetic energy? derive its formula.

Answer 4

the energy possessed by a body due to its motion.

FTB book

formula shows K.E possessed by a body of mass m moving with velocity v.

Question 5

what is P.E? derive its formula? unit?

Answer 5

the energy possessed by a body due to its position or change in configuration.
Joule

Question 6

what is gravitational potential energy?

Answer 6

the energy possessed by an object due to a change in its position when it is present in a gravitational field.

by doing work against force of gravity, an object has been given a special form of P.E called gravitational P.E

Question 7

name & describe all forms of energy?

Answer 7

7

Question 8

what is chemical energy? examples?

Answer 8

energy stored in a substance that is released through a chemical reaction.
fuels and food.
they have chemical energy & when they burn (chemical reaction), they release energy in the form of heat & light

food is fuel (chemical energy), inside the body it releases energy in the form of ATP and release heat

Question 9

what is mechanical & heat energy? examples?

Answer 9

the energy possessed by a body both due to its motion or position. examples: water fall, wind, a moving car, a lifted hammer, a stretched bow, a catapult, compressed spring.
heat energy is given out by hot bodies.
burning fuel. frictional force, food intake, sun

Question 10

define light & sound energy? examples?

Answer 10

a kind of kinetic energy with the ability to make types of light visible to human eyes. plants produce food in the presence of light. candles, bulb, burning fuel, sun.
S.E is produced by vibrations.
examples: vibrating diaphragm of drum, vibrating strings of sitar & vibrating air column of wind instruments such as flute.

Question 11

define E.E and N.E? examples?

Answer 11

widely used form of energy.
supplied by wires. examples: batteries & electric generators. electric generators are run by hydro, thermal or nuclear power.
N.E is released in the form of nuclear radiations. H.E released during nuclear reactors is converted to electrical energy. The energy coming from the Sun is the result of nuclear reactions taking place in the Sun.

H.E released by nuclear reactions converted into E.E

Question 12

example of interconversion of energy?

Answer 12

page 127
heat energy from sun taken by oceans. thermal energy causes water to evaporate to form water vapors. These vapors forms clouds.

Question 13

state the law of conservation of energy?

Answer 13

the amount of energy is neither created nor destroyed, it can only be transformed from one form to another, but the total amount of energy remains constant.

Question 14

2 examples of interconversion of energy?

Answer 14

generation of electricity:
a cyclist going up to the top of a hill.

Question 15

what is dissipated energy?

Answer 15

Any energy that is not transferred to useful energy stores is said to be wasted because it is lost to the surroundings.

aka lost energy= not used in anything

Question 16

all of the energy we get comes directly or indirectly from ______________.
can work done be -ve?

Answer 16

the Sun
yes, if the object is moving in the opposite direction to the direction of the applied force. cos 180 = -1. so the angle should be 180 for the work to be -ve

Question 17

what are fossil fuels?

Answer 17

Fossil fuels are made from decomposing plants and animals. These fuels are found in Earth’s crust and are usually hydrocarbons which can be burned for energy. Coal, oil, and natural gas are examples of fossil fuels

Question 18

what is oil? why is oil preferred source of energy over coal?

Answer 18

oil/crude oil refines into many different energy products such as gasoline/petrol, jet fuel, heating oil
because oil produces more energy than same amount of coal.

oil=crude oil
gasoline=petrol
petroleum= curde version of petrol

Question 19

methane is a __________.

Answer 19

natural gas which is byproduct of oil.
advantage of natural gas: easy to transport

typically natural gases are mixture of gases.

byproduct: a secondary product made in the manufacture of something.

Question 20

what happens when fossil fuels are burnt?
C+O=
hydrocarbon+ O=

Answer 20

they combine with O from the air. The carbon become CO2 hydrogen becomes water. while energy is released as heat.
CO2 + heat energy
CO2 + H2O+ heat energy

Question 21

where does energy come from in nuclear power plants?

Answer 21

In nuclear power plants, we get energy as a result
of fission reaction.
During fission reaction, heavy atoms, such as Uranium atoms, split up into smaller parts releasing a large amount of energy.
Nuclear power plants give out a lot of nuclear radiations and vast amount of heat.
A part of this heat is used to run power plants while lot of heat goes waste into the environment.

Question 22

name renewable energy sources.

Answer 22

Solar energy from the sun.
Hydropower from flowing water.

sunlight & water

Question 23

how can energy be obtained from water?

Answer 23

Dams serve meany purposes. They help to control floods by storing water. The water stored in dams can be used for irrigations & also create electrical energy.

Question 24

how can energy be obtained from the sun?

Answer 24

the energy from direct sunlight can be used to produce electricity. Solar cells are used to power everything. But just like wind energy, significant land area is required to produce large amounts of electricity.

Question 25

define solar and wind energy?

Answer 25

energy coming from the sun (heat and light).
electrical energy obtained from harnessing the wind to turn wind turbines. The K.E of the wind can be used to turn turbine which in turn produces electricity.

FTB book page 152

W.E & S.E requires large open space.

Question 26

what is solar cell? diff/ b/w solar cell & solar panel? what is solar panels used in?

Answer 26

solar energy can be converted directly into electricity by solar cells. A solar cell is made of silicon wafer. When sunlight falls on a solar cell, it converts light into electrical energy.
Larger numbers of solar cells are wired together to form solar panels.

solar panels can provide power to telephone booths, light houses, scientific research centers, satellites.

Question 27

what is geothermal energy? how can we use it?

Answer 27

thermal energy generated & stored in the Earth’s crust.
It can be used for heat or to generate electricity.
geothermal wells are built by drilling deep near hot rock at places. Water is pushed down into the well to (the rocks )quickly heat it & change it into steam. As this gasesous steam rises, the gas turn turbines which drives the generator to produce electricity.

Water is pushed down into the well & then pumped back to the earth. heat

geo: in Earth thermal: thermal energy
geothermal: thermal energy in Earth.

Question 28

describe solar house heating? It consists of what?

Answer 28

a solar collector made of glass panels over blank metal plates absorb the sun’s energy which heats the liquid flowing in the pipes at the back of the collector.
The hot water can be used for cooking, washing and heating the buildings

a collector
a storage device
a distribution system

Question 29

what is biomass? bio-energy? how can we use this energy?

Answer 29

material from which we get bio-energy. Biomass contains stored chemical energy from the sun that is produced by plants by photosynthesis.
bio-energy: energy from living things
by eating
by burning methane which produces electricity, NH4 which is made by animal dung.

Question 30

show block diagram of production of electricity from fossil fuels?

Answer 30

pg 133

Question 31

show energy flow diagrams used of energy saver lamp, vehicle running, power station.

Answer 31

pg 135

Question 32

why can’t input energy be equal to output energy?
a loss in the ____ of body can provide ______________.

Answer 32

because work must be done against frictional forces that causes heat, noise etc
mass
a lot of energy

Question 33

what is efficiency? formula? unit?

Answer 33

ratio of useful energy output to the total energy input.
% efficiency= useful energy output/total energy input x 100

it has no unit as it is the ratio of same quantities so units cancel.

Question 34

define power? unit? quantity? formula? bigger units of power?
unit symbol of watt?

Answer 34

power is the rate at which energy is transferred / the rate at which work is done.
watt (W)
scalar

P= W/t = E/t

1kW= 1000 W
1MW= 1,000,000 W
1hp = 746 W

J/s

Question 35

define 1 watt?

Answer 35

one joule of energy used in one second.
one joule of work done in 1 second.

Question 36

how to write watts in terms of hp? example: 80 watts

Answer 36

1hp = 746 watts
1 watt= 1/ 746=
80 watt= 80/746
0.11 hp

divide it by 746

Question 37

why is only horizontal component of the force acting on the body involved in expression of work?

Answer 37

Since, work will be measured in the direction in which the force acts, the horizontal component is taken into consideration and not the vertical component.

Question 38

a bulb has efficiency of 60%. what does it mean?