Answer to Question #278689 in Physics for ZAR

Question

It is 1.5km from your hostel to the lab.As part of your physical fitness program, you should run that distance at 10Km/hr which uses up energy at the rate of 700Watt or you could walk at 3 Km/hr which uses 290watt energy.which choice would burn more energy..??and how much energy would it burn in joules.?

Answer 1

1.5 km at 10 km/h will take 0.15 h, or 9 min.

1.5 km at 3 km/h will take 0.5 h, or 30 min.

The energy is power times time:

$$E=Pt.\\ E_1=700·(9·60)=378000\text{ J},\\ E_2=290·(30·60)=522000\text{ J}.$$

Running at 10 km/h is more energy-efficient.