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As the drawing illus trates, two disks with masses m1 and m2 are moving horizont

ID: 2138422 • Letter: A

Question

As the drawing illustrates, two disks with masses m1 and 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

Because linear momentum is conserved, Pf = Po so (m1 x vf1) + (m2 x vf2) = (m1 x vo1) + (m2 x vo2)
Therefore, (1.2 x 0) + (2.4 x vf2) = (1.2 x 5) + (2.4 x 5)
2.4 x vf2 = 18
vf2 = 7.5 m/s