Question

A railroad car of mass 18800 kg moving at
3.85 m/s collides and couples with two coupled railroad cars, each of the same mass as
the single car and moving in the same direction at 2.31 m/s.

How much kinetic energy is lost in the collision?
Answer in units of J.

Answer 1

Let mass of the single railroad car is and masses of those coupled railroad cars are and

Let the initial velocities of these cars are , and and the final velocity is .

From momentum conservation law,

but and

So,

Here and

Now the kinetic energy before collision,

(as )

Mass of the cars m= 18800 kg

After collision the final kinetic energy,

So change in kinetic energy ,

∆(KE) = =-15.4 kJ

∆(KE)=-15.4 kJ

-ve sign indicate the loss of energy.

So the kinetic energy lost is 15.4 kJ

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