Question

A hockey puck B rests on frictionless, level ice, and is struck by a second identical puck A, which was originally moving at 50 m/s and is deflected at 30 degrees from its original direction. Puck B acquires a velocity at a 45 degree angle in the other direction. (Let the mass of the puck be m)

A) Find the speed of each puck after the collision.

B) What fraction of the original kinetic energy of puck A disipates during the collision? (As a decimal)

Answer 1

In the figure is shown the problem. We need to establish the conservation of linear momentum before the collition and after the collition. This kind of collition is elastic implying that also need to consider the conservation of the energy. Let's begin with the momentum conservation.

Before the collition the total momentum is

Considering that the second mass is at rest the second them of the initial momentum in x is zero. The total inital momentum in y direction is zero because we only have motion in x direction. The linear momentum after the collition is

Here we denote u as a velocity vector after the collition and have two components. The u vectors can be expressed as

replasing into the final momentum expresions we have

Considering that the final and initial momentum is conserved we have

solving this two equations we have

and therefore

and then

and then

the fraction of the original energy that is disipated can be obtained from