Dr. J's Maths.com
Where the techniques of Maths
are explained in simple terms.

Measurement - units of energy related to people.
Test Yourself 1.


 

Conversion of units.  
   
   
   
Energy for mass and nutrition  
   
   
Energy expended in activities. 7.
Walking speed KJ used in 30 mins.
3 km/h 5.53 kJ/kg
5 km/h 7.37 kJ/kg

Here we must balance the kilocalories consumed against the reduction in energy due to walking.

1. Kilocalories consumed = 73 × 4.184 = 305.432 kJ

2. Energy used in 30 mins - 5.53 × 65 = 359.45 kJ

Hence the fraction of the energy used in 30 mins to be used because of the (delicious) coffee is:

So 0.85 × 30 mins = 25.5 mins

Could round this to 26 mins (to be sure).
 

8. We need to bring the two energy measurements - for the burgers and the run - to the same unit.

It is easier to bring the total kilocalories to kilojoules because of the conversion given.

So as 1 kilocalorie = 4,184 kilojoules, multiply both sides by 85 to find the number of kilojoules Sutarman uses each kilometre. Hence 85 × 4.184 = 355.64.

Assume Sutarman runs k kilometres - he then uses 355.64 k kilojoules.

But his burgers contained 2 × 970 = 1,940 kilojoules.

∴ equate these: 355.64 k = 1940.

Divide both sides by 355.64 gives k = 5.45.
So Sutarman needs to run 5.5 km.