#18? 18. As the drawing illustrates, two disks with masses m1and m2, are moving

Question

#18? 18. As the drawing illustrates, two disks with masses m1and m2, are moving horizontally to the right at a speed of v0. They are on an air-hockey table, which supports them with an essentially frictionless cushion of air. They move as ,a unit, with a compressed spring between them, which has a negligible mass. Then the spring is released and allowed to push the disks outward. Consider the situation where disk 1 comes to a momentary halt shortly after the spring is released. Assuming that m1 = 1.2 kg, m2 = 2.4 kg, and v0 = +5.0 m/s, find the velocity of disk 2 at that moment.

Explanation / Answer

Use the law of conservation of linear momentum to find the velocity of mass m2.

            (m1+m2)v0 = m2v

Therefore, the velocity of the mass m2 is,

           v = [(m1+m2)v0] / m2

              = [(1.2 kg + 2.4 kg)(5.0 m/s) / (2.4 kg)]

              = 7.5 m/s

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