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Two ice skaters, Daniel (mass 60.0 kg ) and Rebecca (mass 45.0 kg ), are practicing. Daniel stops to tie his shoelace and, while at rest, is struck by Rebecca, who is moving at 14.0 m/s before she collides with him. After the collision, Rebecca has a velocity of magnitude 6.00 m/s at an angle of 55.1 ∘ from her initial direction. Both skaters move on the frictionless, horizontal surface of the rink.

A) What is the magnitude of Daniel's velocity after the collision?
B) What is the direction of Daniel's velocity after the collision?

Respuesta :

Momentum p = mv before the collision equals the momentum after the collision since there are no external forces acting on the two ice skaters.

Let's say Rebeccas is moving in the x positive direction before the collision and:
Rebecca's mass m₁ = 45 kg
Daniel's mass m₂ = 60 kg

p = m₁v₁ + m₂v₂ 

before the collision:
x: p = 45 * (+14) = 630
y: p = 0

after the collision:
x: p = 630 = 45 * 6 * cos 55.1 + 60 * v₂ ⇒ v₂ = 7.9
y: p = 0 = 45 * 6 * sin 55.1 + 60 * v₂⇒ v₂= -3.7

|v| = 8.7
∡v = -25°

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