
William W. answered 03/04/19
Experienced Tutor and Retired Engineer
This seems like it should be a two dimensional problem because you envision the ball and pin having the ability to move in any direction, however, all motion is occurring to the right therefore, it is really a 1 dimensional problem - there is no motion in any direction but to the right.
The momentum before the collision is given by P1 = (mball)(vball) + (mpin)(vpin) = (6.0)(3.5) + (0.70)(0) = 21 kgm/s and the momentum immediately after the collision is given by P2 = (mball)(vball) + (mpin)(vpin) = (6.0)(2.77) + (0.70(vpin).
Due to the conservation of momentum, P1 = P2 so 21 = (6.0)(2.77) + (0.70(vpin).
21 = 16.62 +0.70vpin
4.38 = 0.70vpin
vpin = 6.3 m/s to the right