Conservation of Momentum


Ex) 12,600 kg railroad car travels on a frictionless surface with a constant speed of 18.0 m/s. A 5350 kg load at rest is dropped onto the car, what will the car's new speed be?


Total momentum before = total momentum after

m1v1 = m2v2






V2 = 12.6 m/s


Ex) An atomic nucleus moving at 420 m/s emits an alpha particle in the direction of its motion and the remaining nucleus slows to 350 m/s.

If the alpha particle has a mass of 4.0 µ and the original nucleus has a mass of the 222 µ, what speed does the original alpha particle have when it is emitted?



No need to convert mass to kg. Why?



Original nucleus = mass = 222 µ,

v =  420 m/s


alpha particle  = mass of 4.0 µ

v = ?

New Nucleus = 218 µ  (alpha lost)

v = 350 m/s

Speed of original alpha particle have when it is emitted?


mom nucleus = mom alpha + mom new nucleus

mv = mava + mnvn



v = 4.2 x 103 m/s




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