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As the drawing illustrates, two disks with masses m 1 and m 2 are moving horizon

ID: 1264015 • 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 airhockey 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 = 1.4 kg, m2 = 2.0 kg, andv0 = +5.0 m/s, find the velocity of disk 2 at that moment.

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 airhockey 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 = 1.4 kg, m2 = 2.0 kg, andv0 = +5.0 m/s, find the velocity of disk 2 at that moment.

Explanation / Answer

Since linear momentum is conserved, Pf = Po.

so, we have

       (m1 x vf1) + (m2 x vf2) = (m1 x vo1) + (m2 x vo2)
Therefore, the velocity of disk 2 is,

          (1.4 x 0) + (2.0 x vf2) = (1.4 x 5.0) + (2.0 x 5.0)
                  2.0 x vf2 = 17
                                       vf2 = 8.5 m/s