work energy and power

Question 1

what is the equation for work done

Answer 1

work done = force x distance moved in the direction of force
W=Fx

Question 2

what is work done

Answer 2

force x distance moved in the direction of force

Question 3

what is the unit for work done

Answer 3

Nm or J

Question 4

what is a joule

Answer 4

the work done when a force of 1N moves its point of application 1m in the direction of the force

Question 5

what is work done the same as

Answer 5

energy transferred

Question 6

when force is applied to the angle of an object how do you calculate the work done

Answer 6

work done = Fcos0 x x

Question 7

is work done a vector or a scalar

Answer 7

scalar

Question 8

what is the base unit of a joule

Answer 8

J
Nm
(kgm)/s^2 m
kgm^2s^-2

Question 9

what is energy

Answer 9

the capacity for doing work

Question 10

is energy a vector or scalar quanitity

Answer 10

scalar

Question 11

what is the unit for energy

Answer 11

Joule J

Question 12

what are the forms of energy

Answer 12

kinetic
gravitational potential
chemical
elastic potential
electrical potential
nuclear
radiant/electromagnetic
sound
internal/heat/thermal

Question 13

what is kinetic energy

Answer 13

energy due to motion of an object with mass

Question 14

what is gravitational protentional energy

Answer 14

energy of an object due to its position in a gravitational feild

Question 15

what is chemical energy

Answer 15

energy contained within the chemical bonds between atoms - it can be released when the atoms are rearranged

Question 16

what is elastic potential energy

Answer 16

energy stores on an object as a result of reversible change in its shape

Question 17

what is electrical energy

Answer 17

energy of electrical charges due to their position in an electric field

Question 18

what is nuclear energy

Answer 18

energy within the nuclei of atoms - it can be released when the particles within the nucleus are rearranged

Question 19

what is radiant/electromagnetic energy

Answer 19

energy associated with all electromagnetic waves, stored within the oscillating electric and magnetic feilds

Question 20

what is sound energy

Answer 20

energy of mechanical waves due to the movement of atoms

Question 21

what is internal/heat/thermal energy

Answer 21

the sum of the random potential and kinetic energies of atoms in a system

Question 22

what is the principle of conservation of energy

Answer 22

the total energy of a closed system remains constant; energy can never be created or destroyed but it can be transferred from one form to another

Question 23

what is the equation for kinetic energy

Answer 23

EK=1/2mv^2

Question 24

how do you derive the equation for kinetic energy

Answer 24

W=fs
from newtons second law know F=ma
W=mas
also assume what the body has been accelerated from rest u=0 to a velocity v while covering distance s then
v^2=u^2+2as
but as u=0
v^2=2as
rearrange for as
as=v^2/2
therefore W=mas=mv^2/2
as work done is entirely transferred to the Ek of the object the work done = energy transferred
Ek=1/2mv^2

Question 25

what does the equation for kinetic energy tell us

Answer 25

for objects travelling at the same speed the KE is directly proportional to the mass for a given object the KE is directly proportional to the square of its speed

Question 26

what is the equation for gravitational potential energy

Answer 26

EP=mgh

Question 27

when an objects et higher what happens to it GPE

Answer 27

it is gained lost when an object gets lower

Question 28

how do you drive the equation for gravitational protentional energy

Answer 28

W=Fs if a body moves upwards at a constant velocity there must be some upward force acting on it to balance the weight (mg) of the object acting vertically downwards therefore F=mg W=mgs body moves a distance (s) vertically upwards this would be described as a change in height (h) therefore s=h W=mgh as a speed has remained constant then all the work done can be assumed to have transferred to the gravitational potential energy sore of the body therefore EP=mgh

Question 29

why is the braking distance (s) of a car directly proportional to its initial speed squared

Answer 29

Fs=1/2mv^2 all of the vehicles kinetic energy must be dissipated by the brakes in order to come to a stop

Question 30

when KE and GPE are exchanged how do the equations interact

Answer 30

mgh=1/2mv^2 where v is the final speed of the object the mass m on both sides cancels out as it is the same gh=1/2v^2 v^2=2gh v=square root 2gh equation only valid when no resistive forces involved

Question 31

what is power

Answer 31

rate of work done/rate of energy transferred

Question 32

what is the equation of power

Answer 32

Power = work done/time P=W/t

Question 33

what is the unit of power

Answer 33

Js^-1 watts W

Question 34

what can power be used with motion

Answer 34

constant force has to be exerted on an object to maintain a constant speed

Question 35

what is the equation of power for motion

Answer 35

power = force x speed (constant) P=Fv

Question 36

how do you derive the power and motion equation P=Fv

Answer 36

W=Fs P=W/t P=Fs/t s/t (displacement/time) is velocity P=Fv

Question 37

how do you calculate efficienct

Answer 37

efficiency = useful output energy/total input energy x100 or efficiency = useful output power/total input power x 100

Question 38

why do you have to calculate effiecienct

Answer 38

never transfer 100% of input energy into useful output energy - energy is always 'wasted' by transfers into other forms e.g. heat