A railroad flatcar of weight 7840 N can roll without friction along a straight h

Question

A railroad flatcar of weight 7840 N can roll without friction along a straight horizontal track. Initially, a man of weight 612 N is standing on the car, which is moving to the right with speed 25 m/s; see the figure. What is the change in velocity of the car if the man runs to the left so that his speed relative to the car is 5.5 m/s?

A railroad flatcar of weight 7840 N can roll without friction along a straight horizontal track. Initially, a man of weight 612 N is standing on the car, which is moving to the right with speed 25 m/s; see the figure. What is the change in velocity of the car if the man runs to the left so that his speed relative to the car is 5.5 m/s?

Explanation / Answer

weight of flatcar = 7840 N

mass of flatcar = 7840 /g

weight of man = 612 N

mass of mass = 612/g

initial speed of flatcar + man = 25 m/s

total initial momentum = (mass of flatcar + mass of man) initial velocity = ((7840 /g )+ (612/g))25

total initial momentum = 211300/g

momentum of man = mass of man x velocity = (612/g)*5.5 = 3366/g

final momentum = initial momentum + momentum of man

(mass of flatcar + mass of man) final velocity = 211300/g + 3366 /g

(8452/g) Vf = 211300/g + 3366 /g

Vf = 25.465 m/s

change in velocity = 25.465 m/s - 25 = 0.465 m/s

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