The Anonymous Widower

Calculating Kinetic And Potential Energies

I used to be able to do this and convert the units, manually and easily, but now I use web calculators.

Kinetic Energy Calculation

I use this kinetic energy calculator from omni.

Suppose you have a nine-car Crossrail Class 345 train.

  • It will weigh 328.40 tonnes, according to my detective work in Weight And Dimensions Of A Class 345 Train.
  • There will be 1,500 passengers at 90 Kg. each or 135 tonnes.
  • So there is a total weight of  463.4 yonnes.
  • The train has a maximum speed of 90 mph.

Put this in the calculator and a full train going at maximum speed has a kinetic energy of 104.184 kWh.

The lithium-ion battery in a typical hybrid bus, like a New Routemaster has a capacity of 75 kWh.

So if a full Class 345 train, were to brake from maximum speed using regenerative braking, the energy generated by the traction motors could be stored in just two bus-sized batteries.

This stored energy can then be used to restart the train or power it iin an emergency.

Out of curiosity, these figures apply to an Inter City 125.

  • Locomotive weight – 2 x 70.25 tonnes
  • Carriage weight – 8 x 34 tonnes.
  • Train weight – 412.5 tonnes
  • Passengers – appromiximately 700 = 63 tonnes
  • Speed – 125 mph

This gives a kinetic energy of 206.22 kWh

And then there’s Eurostar’s original Class 373 trains.

  • Weight- 752 tonnes
  • Speed 300 kph

This gives a kinetic energy of 725 kWh.

If a 75 kWh battery were to be put in each of the twenty cars, this would be more than adequate to handle all the regenerative braking energy for the train.

There would probably be enough stored energy in the batteries for a train to extricate itself from the Channel Tunnel in the case of a complete power failure.

Potential Energy Calculation

I use this potential energy calcultor from omni.

Suppose you have the typical cartoon scene, where a ten tonne weight is dropped on a poor mouse from perhaps five metres.

The energy of the weight is just 0.136 kWh.

I’ve used kWhs for the answers as these are easily visualised. One kWh is the energy used by a one-bar electric fire in an hour.

February 9, 2018 - Posted by | World | , , ,

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