25. Converting Energy to Mass. Two freight trains, each of mass 6 x 10^6 kg (6 0

Question

25. Converting Energy to Mass. Two freight trains, each of mass 6 x 10^6 kg (6 000 metric tons) travel in opposite directions on the same track with equal speeds of 150 km/hr. They collide head-on and come to rest. (a) Calculate in joules the kinetic energy (1/2)mv^2 for each train before the collision. (Newtonian expression OK for everyday speeds!) (b) After the collision, the mass of the trains plus the mass of the track plus the mass of the roadbed plus the mass of the surrounding air plus the mass of emitted sound and light has increased by what number of milligrams?

Explanation / Answer

(a)

The formula for kinetic energy is

KE= (1/2 ) mv^2 = ( 1/2) 6 * 10 *6 kg (( 150 km/hr ) ( 1000 m/ 3600 s))^2 = 5208.33 * 10 ^6 J

(b) the given information is not sufficient to calculate the second part.

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