work, energy, power and efficiency

Question 1

what is energy needed for?

Answer 1

Energy is needed to make a stationary object move, to change its shape, or to warm it up

Question 2

examples of energy stores;

Answer 2

gravitational potential stores

kinetic energy stores

thermal energy stores

elastic energy stores

Question 3

what are different ways energy can be transferred

Answer 3

by radiation (light), electrically, mechanically

Question 4

what is energy measured in ?

Answer 4

joules

Question 5

1 ____ is equal to the ______ needed to raise a 1 _____ weight through a ______ height of 1 ______

Answer 5

Energy is measured in joules (J). One joule is equal to the energy needed to raise a 1 N weight through a vertical height of 1 m.

Question 6

what happens when energy is transferred?

Answer 6

Whenever energy is transferred, the total amount of energy after the transfer is always equal to the total amount of energy before the transfer. The total amount of energy is unchanged.

Question 7

what is the principle of conservation of energy?

Answer 7

energy cant be created or destroyed

Question 8

what does it mean when work is done?

Answer 8

work is done on an object when a force acting on it makes a move - energy is transferred to the object

Question 9

what does the amount of work done depend on?

Answer 9

The amount of work done depends on the force and the distance the object moved.

Question 10

greater the _____ or further the ______, ______ the work done

Answer 10

The greater the force or the further the distance, the greater the work done.

Question 11

equation for work done

Answer 11

force x distance moved in direction of force (parallel)

Question 12

unit of work done

Answer 12

joule

Question 13

equation for work done involving an angle?

Answer 13

W = F s cos theta

-s is distance travelled
-theta is angle between direction of the force and direction of motion

Question 14

what does area under force displacement graph represent?

Answer 14

work done

Question 15

how to work out area under graph?

Answer 15

constant/straight line = area of shapes such as triangle/square

variable-counting squares

Question 16

what is kinetic energy

Answer 16

energy an object has due to its motion

faster an object moves the more kinetic energy it has

Question 17

equation for kinetic energy?

Answer 17

1/2mv^2

Question 18

what is potential energy?

Answer 18

energy an object has due to its position

Question 19

equation for graviatational potential energy?

Answer 19

Mgh
mass x gfs x change in height

Question 20

how does the work done affect gravitational potential energy?

Answer 20

work done on the object increases gravitational potential energy

Question 21

what can you do with KE equation and PE equation if air resistance is negligible

Answer 21

Consider an object of mass m released above the ground.

If air resistance is negligible, the object gains speed as it falls.

Its potential energy therefore decreases and its kinetic energy increases.

After falling through a vertical height ∆𝒉, its kinetic energy is equal to its loss of potential energy:

𝟏 𝒎𝒗𝟐 = 𝒎𝒈∆𝒉

Question 22

what are the ways of transferring energy from one object to another?

Answer 22

work done ( work done by a force due to one object making other object move)

heat transfer ( heat transfer from a hot object to cold object - conduction, convection, radiation)

electromagnetic waves

Question 23

definition of power

Answer 23

rate of transfer of energy

Question 24

unit for power

Answer 24

watt

equal to energy transfer rate of 1 joule per second

Question 25

equation for power

Answer 25

energy / time or work done/time

Question 26

what is the output power of an engine called?

Answer 26

motive power

Question 27

what happens when a powered object moves at a constant velocity at a constant height?

Answer 27

When a powered object moves at a constant velocity at a constant height, the resistive forces (e.g., friction, air resistance, drag) are equal and opposite to the motive force.

Question 28

where is the work done in an engine transferred to

Answer 28

The work done by the engine is transferred into the internal energy of the surroundings by the resistive forces.

Question 29

equation for work done for a powered vehicle

Answer 29

P = F V

Question 30

what is useful energy?

Answer 30

energy transferred for a purpose

Question 31

what is wasted energy

Answer 31

not all energy supplied is transferred for intended purpose

Question 32

equation for efficiency

Answer 32

useful energy transferred by machine / energy supplied to machine

or

work done by machine/energy supplied to machine

Question 33

how can we express efficiency

Answer 33

output / input

Question 34

how can efficiency be improved?

Answer 34

how efficient a device/machine is dependent on how much useful energy/power it provides compares to the total input

rest of the energy is dissipated as heat/sound - this can be made more efficient