Work, Power, and Energy

Question 1

factors affecting work done

Answer 1

1. magnitude of force applied
2. displacement produced by the force
   (3. angle between force and displacement)

Question 2

amount of work done is equal to?

Answer 2

the product of the force applied on it and the displacement of the point of application of force, in the direction of force

Question 3

work is scalar/vector

Answer 3

scalar

Question 4

if a force displaces a body in direction other than direction of force, amount of work done can be determined by…

Answer 4

1. finding the component of displacement along the force
2. finding the component of force along the displacement

Question 5

Special cases for work done

Answer 5

1. if displacement is in the direction of force, work done is positive
2. when displacement is normal to the direction of force, work done is 0.
3. if displacement is in a direction opposite to force, work done is negative

Question 6

work done by the force of gravity

Answer 6

work done by the force of gravity is the same whether the body comes down from a certain height using stairs or a slope or lift. if the body goes up, work done is negative

Question 7

define 1 joule

Answer 7

1 joule of work is said to be done when a force of 1 newton displaces a body through a distance of 1 meter in its own direction

Question 8

CGS unit of work

Answer 8

1 erg= 1 dyne * 1 cm

Question 9

1 joule is how many erg

Answer 9

1 joule= 10^7 erg

Question 10

define power

Answer 10

the rate of doing work (scalar)

Question 11

power depends on

Answer 11

1. amount of work done by the source
2. time taken by the source to do said work

Question 12

power is also equal to

Answer 12

force * average speed

Question 13

SI and CGS unit of power

Answer 13

watt (W)
erg per second

Question 14

define 1 watt

Answer 14

if 1 joule of work is done in 1 second, power spent is 1 watt

Question 15

1 watt is how many erg per sec

Answer 15

1 W = 10^7 erg per second

Question 16

1 HP is how many watts

Answer 16

1 HP= 746 W= 0.746 kW

Question 17

define energy

Answer 17

the capacity of a body to do work (scalar)

Question 18

when is there no transfer of energy

Answer 18

when a body is acted upon by a force normal to the direction of displacement

Question 19

units of energy

Answer 19

SI: joule
CGS: erg
bigger units: watt hour. kilowatt hour
for heat energy: calorie
Electron volt

Question 20

define 1 Wh

Answer 20

1 watt hour is the energy spent by a source of power 1 W in 1 hr

Question 21

define 1 calorie

Answer 21

1 calorie is the heat energy required to raise the temperature of 1 g of water by 1 degree C

Question 22

1 calorie is how many J

Answer 22

1 cal= 4.18 J
1 J= 0.24 cal

Question 23

what is electron volt

Answer 23

the energy transfer in case of atomic particles is very small, so it is measured in electron volt eV

Question 24

define 1 eV

Answer 24

1 eV is the energy gained by an electron when it is accelerated through a potential difference of 1 V

Question 25

how many joules is 1 eV

Answer 25

1 eV= 1.6 * 10^-19 J

Question 26

define potential energy

Answer 26

the energy possessed by a body at rest due to its position or size and shape is called potential energy

Question 27

kinds of potential energy

Answer 27

1. gravitational potential energy (negative) 2. elastic potential energy

Question 28

gravitational PE of a body at a point

Answer 28

work done by force of attraction of the earth in getting that body from infinity to that point. OR the amount of work done in lifting that body at a height against force of gravity

Question 29

define kinetic energy

Answer 29

the energy possessed by a body due to its state of motione

Question 30

expression of KE

Answer 30

the KE possessed by a moving body is equal to the amount of work which the moving body is capable of doing before coming to rest.

Question 31

KE and momentum are related as

Answer 31

KE= p^2/ 2m

Question 32

work-energy theorem

Answer 32

the increase in kinetic energy of a moving body is equal to the work done by a force acting in the direction of the moving body.

Question 33

three forms of KE

Answer 33

1. translational (straight line) 2. rotational (rotating about an axis) 3. vibrational (to and fro from a mean position)

Question 34

forms of energy

Answer 34

1. solar 2. heat 3. hydro 4. light 5. chemical 6. electrical 7. mechanical 8. nuclear 9. wind

Question 35

define light energy

Answer 35

it is a form of energy in the presence of which other objects are seen

Question 36

define electrical energy

Answer 36

when two dry bodies are rubbed together, they get charged due to the movement of free electrons from one body to the other body.

Question 37

define nuclear energy

Answer 37

the energy released due to loss in mass during the processes of nuclear fission and fusion, is called nuclear energy.

Question 38

define geothermal energy

Answer 38

the energy released in nuclear disintegrations in the interior of earth, gets stored deep inside and is called geothermal energy.

Question 39

principle of conservation of energy

Answer 39

energy can neither be created nor be destroyed. it only changes from one form to another.