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# A 12,600kg railroad car travels along on a level frictionlesstrack with a constant speed of 18.0 m/s. A 5,350kg load,initially at rest is dropped onto the car. What will be thecars new speed?

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A 12,600kg railroad car travels along on a level frictionlesstrack with a constant speed of 18.0 m/s. A 5,350kg load,initially at rest is dropped onto the car. What will be thecars new speed?

That is,$$\displaystyle{m}_{{{1}}}{v}_{{{1}}}={\left({m}_{{{1}}}+{m}_{{{2}}}\right)}{v}_{{{2}}}$$
Hence $$\displaystyle{v}_{{{2}}}={m}_{{{1}}}\frac{{v}_{{{1}}}}{{{m}_{{{1}}}+{m}_{{{2}}}}}={12600}\times\frac{{18}}{{17950}}={12.6}\frac{{m}}{{s}}$$