# 3-5 Calculations (p 116 3.2)

Calculations (p 116) 3.2
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Slide 1: Tekstslide
NatuurkundeMiddelbare schoolhavo, vwoLeerjaar 2

In deze les zitten 21 slides, met interactieve quizzen, tekstslides en 1 video.

Lesduur is: 50 min

## Onderdelen in deze les

Calculations (p 116) 3.2

#### Slide 2 -Video

Energy
• During combustion energy is released in the form of heat and light.
• Your body also releases energy during the combustion of food. This is used to move and to heat up the body.

#### Slide 3 -Tekstslide

Joule
Energy is measured in joule (J).
1 joule is a very small quantity so we rather work in kJ and MJ
1 kJ = 1 000 J
1MJ = 1 000 000 J

#### Slide 4 -Tekstslide

Energy
• Walking up one fight of stairs uses = 10 kJ
• Running 1 km = 200kJ
• 20% of energy used is by the brain
• 14 year old person uses about
11 000 kJ per day.
• Boys use a bit more.

#### Slide 5 -Tekstslide

Food
• On the label of food it is written how much energy is released during combustion.
• 100 gram penutbutter = 2 690 kJ
• Energy in food is also
indicated in the unit
kilocalories (kcal)
1kcal = 4,2 kJ

#### Slide 6 -Tekstslide

Heat of combustion
• 1kg dry wood releses 16 MJ heat
• 1kg coal releases 29 MJ heat/ energy
• Heat of combustion -
The amount of energy that is released when buring 1kg
of fuel.
• Liquids are measured in liters and gasses in m3

#### Slide 7 -Tekstslide

Natural gas
Hydrogen gas
Petrol
Diesel
Dry wood
Coal
Type of fuel                          Ammount.                           Energy                 HEAT of combus.

#### Slide 8 -Tekstslide

Calculations using the table
How much energy is released when you burn 20 kg of dry wood?
(from the table you see the heat of combustion = 16 MJ)

Therefore it will be 16 x 20 = 320 MJ
Amount
1kg
20 kg
Heat
16 MJ
?

#### Slide 9 -Tekstslide

Energy in food
• This is mostly indicated per 100 gram (kJ/100g) and liquids in kJ/100ml
• Nutritional value=  heat of combustion of food
• Of all the food you eat the body uses:
Carbohydrates, fats and protein
• 1g protein/ carbohydrate = 17kJ
• 1g fat = 38 kJ

#### Slide 10 -Tekstslide

Nutritional value is the same as heat of combustion.
A
true
B
false

#### Slide 11 -Quizvraag

1kcal equals 4,2 kJ
A
true
B
false

#### Slide 12 -Quizvraag

The body uses carbohydrates, fats and hydrocarbons in foods.
A
true
B
false

#### Slide 13 -Quizvraag

The heat of combustion of a fat is higher that that of a hydrocarbon.
A
true
B
false

#### Slide 14 -Quizvraag

One liter of petrol has more energy than one liter of diesel.
A
true
B
false

Convert:
0,85 MJ =
A
0,000 85 kJ
B
0,85 kJ
C
850 kJ
D
850 000kJ

Convert:
250 000 J =
A
250 000 MJ
B
250 MJ
C
0,25 MJ

730 J =
A
730 000 kJ
B
730 kJ
C
0,73 kJ
D
0,000 73 kJ

#### Slide 18 -Quizvraag

Now do the following questions
29, 31, 32, 33 (blz 117)

Of question 31 insert a picture on the next slide.