Two ice skaters, Daniel (mass 70.0 ) and Rebecca (mass 45.0 ), are practicing. D

Question

Two ice skaters, Daniel (mass 70.0 ) and Rebecca (mass 45.0 ), are practicing. Daniel stops to tie his shoelace and, while at rest, is struck by Rebecca, who is moving at 14.0 before she collides with him. After the collision, Rebecca has a velocity of magnitude 8.00 at an angle of 55.1 from her initial direction. Both skaters move on the frictionless, horizontal surface of the rink. What is the magnitude of Daniel's velocity after the collision? What is the direction of Daniel's velocity after the collision? degrees from Rebeccas original direction.

Explanation / Answer

I guess you're supposed to assume the collisions are elastic - physics teacher has a sense of humor. For most actual ice skaters, the collisions wouldn't be elastic, meaning some energy would be absorbed by the skaters and transformed to other forms of energy (chemical, heat, sound ...) Based on the last question I wonder if some energy is converted to some other form Assume momentum is conserved. The initial momentum is 70kg*0 + 45kg*12 m/s (assume this is in the positive x direction for utmost simplicity) = 540 kg m/s i and the i is the unit vector in the x direction. After the collision Rebecca's momentum is 45 * 8.0 * Therefore Daniel's momentum is - that vector Divide by his mass to determine his velocity Find the square root of the sum of the squares of the two components to find its magnitude Divide by that to find its direction The change in kinetic energy is the final - the initial The initial is 1/2 (45) (12^2) The final is 1/2 (45) (8^2) + 1/2 (70) (that magnitude^2)

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