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

ID: 2280694 • 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 = 1.3 kg, m2 = 2.4 kg, and v0 = +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 = 1.3 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, (1.3 x 0) + (2.4 x vf2) = (1.3 x 5.0) + (2.4 x 5.0)
2.4 x vf2 = 18.5
vf2 = 7.70834 m/s