SP8: forces doing work

Question 1

when a force causes a body to move, what is being done?

Answer 1

work is being done on the object by the force

Question 2

what is work the measure of?

Answer 2

energy transfer when a force moves an object through a distance

Question 3

work done equation

Answer 3

force × distance

Question 4

units for work done

Answer 4

work done in joules (j)
force in newtons (N)
distance in metres (m)

Question 5

what direction does distance act in?

Answer 5

the same as the force

Question 6

a horizontal force of 50 N causes a trolley to move a horizontal distance of 30 m. how much work is done on the trolley by the force?

Answer 6

1,500 J

Question 7

12,000 J of energy is supplied to move a small truck a distance of 80 m. what is the size of the force applied?

Answer 7

150N

Question 8

kinetic energy equation

Answer 8

1/2 x mass x velocity²

Question 9

units for kinetic energy:

Answer 9

kinetic energy in joules (J)
mass in kilograms (kg)
speed in metres per second (m/s)

Question 10

how much kinetic energy does a 30 kg dog have when it runs at 4 m/s?

Answer 10

240 J

Question 11

change in gravitational potential energy equation

Answer 11

mass × graviational field strength × change in vertical height

Question 12

units of change in gravitational potential energy

Answer 12

change in gravitational potential in joules (J)
mass in kilograms (kg)
gravitational field strength in newtons per kilogram (N/kg)
change in vertical height in metres (m)

Question 13

galileo takes a 5 kg cannonball to the top of the tower of Pisa for one of his experiments. the tower is 56 m high. how much gravitational potential energy has the cannonball gained?
(g = 10 N/kg)

Answer 13

2800 J

Question 14

dissipation

Answer 14

spreading out and transfer of energy stores into less useful forms

Question 15

dissipation in mechanical systems

Answer 15

-energy is dissipated when two surfaces rub together
-work is done against friction which causes heating of the two surfaces
-the thermal energy store of the surfaces increases

Question 16

what is power?

Answer 16

the rate at which energy is transferred

Question 17

the more powerful a device is, the more…

Answer 17

energy it will transfer each second

Question 18

power equations

Answer 18

power = work done/ time taken

triangle = WPT

Question 19

units of power equation

Answer 19

-power in watts (W)
-work done in joules (J)
-time in seconds (s)

Question 20

one watt is equal to…
what does this mean?

Answer 20

-one joule per second
-this means that for every extra joule that is transferred per second, the power increases by one watt

Question 21

two electric motors are used to lift a 2N weight through a vertical height of 10 m

motor one does this in 5 seconds
motor two does this in 10 seconds

Answer 21

1. for both motors, the energy transferred - the work done is 20 J
2. for motor one, power = 4W
   ↳ 20J/5s = 4W
3. for motor two, power = 2W
   ↳ 20J/10s = 2W