A man weighing 70 kg runs alongside railroad tracks with a velocity of 18 km/h, and jumps into a car of weight 100 kg standing on the tracks.
Calculate the velocity with which the car and man will start moving.

Mass of man (m1) = 60kg            

Initial velocity of man (u1) = 18 km/h=18x5/18=5m/s

Final velocity of man (v1) = (v2) = v  

Mass of car (m2)= 100kg

Initial velocity of car (u2) = 0 (as it is in rest)

Final velocity of car (v2) = v

According to law of conservation of momentum,

m1u1 +m2u2 = m1v1 + m2v2

60x5 + 100x0 = 60 x v + 100 x v

300+0 = 160v  

v = 300/160

v = 1.875 m/s

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