Chapter 5 - work energy and power

Question 1

what is an equivalent phrase for work done

Answer 1

energy transferred

Question 2

what is the equation for work done

Answer 2

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

Question 3

how does the equation change if the force is applied at an angle

Answer 3

w = f x cos(theta) x (x)

Question 4

kinetic energy

Answer 4

energy due to the motion of an object with mass

Question 5

GPE

Answer 5

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

Question 6

elastic potential energy

Answer 6

energy stored in an object as a result of a reversible change in shape

Question 7

chemical energy

Answer 7

energy contained within the chemical bonds between atoms

Question 8

electrical potential energy

Answer 8

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

Question 9

nuclear energy

Answer 9

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

Question 10

radiant energy

Answer 10

energy associated with electromagnetic waves

Question 11

sound energy

Answer 11

energy from the mechanical waves of atoms

Question 12

heat energy

Answer 12

the sum of the random potential and kinetic energies of atoms

Question 13

define conservation of energy

Answer 13

” energy can never be created or destroyed, only transferred from one form to another; the energy in a closed system remains constant”

Question 14

equation for kinetic energy

and what proportionality does this give

Answer 14

KE = 1/2 x mass x velocity^2
KE is proportional to velocity^2
KE is proportional to mass

Question 15

equation for GPE and value for g

Answer 15

GPE = m x g x change in height

Question 16

if no resistive forces are present in a situation how can the transfer of GPE–> KE be modelled

Answer 16

mgh = 1/2mv^2
gh = 1/2v^2
v= sqrt(2gh)

Question 17

define power

Answer 17

the rate of work done/energy transfer

Question 18

equation for power (3)

units for power

Answer 18

P = W/t
P = E/t
P= Fv
measured in Js^-1 or watts (W)

Question 19

define efficiency

Answer 19

the proportion of input energy which is transferred to useful energy

Question 20

equation for efficiency

Answer 20

efficiency = (useful output energy/total input energy) x 100

Question 21

what does 1Nm equal

Answer 21

1J

Question 22

when do we tend to use the equation for power of P = fv

Answer 22

for an object moving at a constant velocity against a constant resistive force

Question 23

what is energy

Answer 23

the capacity of an object to do work on another object

Question 24

briefly describe how to calculate power for a motor lifting a load

Answer 24

• measure mass of load using a mass balance
• calculate weight of load using w = mg
• use the motor to lift the load
• measure the time taken using a stopwatch
• calculate power using (change in GPE)/time