As the drawing illustrates, two disks with masses m1 and m2 are moving horizonta

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 = 1.3 kg, m2 = 2.7 kg, and v0 = 6.5 m/s, find the velocity of disk 2 at that moment.

Drawing- http://www.webassign.net/cj8/7-p-018.gif

Explanation / Answer

Because linear momentum is conserved,

Pf = Po

(m1 x vf1) + (m2 x vf2) = (m1 x vo1) + (m2 x vo2)
Therefore, (1.3 x 0) + (2.7 x vf2) = (1.3 x 6.5) + (2.7 x 6.5)
2.7 x vf2 = 26
vf2 = 9.63 m/s

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