In: Physics
If a coal-fired power plant burns 2 kg of coal to produce electricity, and the electricity is used to power an elevator motor that is 60% efficient, how high can the elevator and passengers be lifted up if their total mess is 1500 kg?
and then How many human workers using muscle power('energy servants") would be needed to lift the elevator up to the same height, if they had one minute to do so?
Assuming that one energy servant is 100w of energy and the coal power plant is 33% efficient. ANd 29MJ/kg in coal
Energy obtained by burning 2kg of coal at 60 percent efficiency is
The energy required to lift 1500 kg of elevator by height h is
Equating these 2 energies
Therefore the height reached by the elevator is
Each energy servant produces 100 W of power
Then equating the energy of n servants for 1 minute with 33 percent efficiency to the energy required to raise the elevator we get
This gives the number of workers as