 Recently, there is a spate of MRT incidents and one of them involved a train collision on 15 Nov 2017.

Learning Physics has practical uses in the real world. The collision of the 2 trains is a case in point. Every day we take many things for granted. When a train moves, it generates an enormous amount of energy. In order for it to stop smoothly and safely, the timing and the braking force must be precise. All these calculations of the forces require an understanding of Physics.

Someone sent me some questions regarding the physics of the collision. See diagram on the left. There are 2 questions in the diagram. If you are an O-Level Physics student, would you like to solve these problems yourself?

Below are my proposed solutions:

Q1a:

Work done in stopping train = Loss in kinectic  energy of train

Retarding Force x stopping distance = ½ x mass x (velocity)2
Retarding Force x 5 = ½ x 140,000 x 202
Therefore Retarding Force = 5,600,000N

Q1b:
20W =0.020kW
15 mins =0.25 hr
Total kWh = (0.020×0.25) x (2.5×106) = 12,500 kWh
Total Cost = 12,500 x 0.15 = \$1,875