Posted by Elisa on Monday, July 7, 2008 at 9:33am.
If the girl is walking at 1.45 m / s in the x direction relative to the plank and the plank is moving at velocity V in the x direction then her total velocity is 1.45 + V in the x direction. (note - V better come out negative, in the negative x direction in part b)
There are no external horizontal forces on this system.
Therefore there will be no change in the initial horizontal momentum, which is zero.
final momentum:
0 = 45 * (1.45+V) + 163 V
0 = 65.25 + 45 V + 163 V
208 V = - 65.25
V = -0.314 m/s
by the way that means the girl is going at 1.45 -.314 = 1.14 relative to the ice and as a check in the ice coordinate system
0 = -0.314 * 163 + 1.14 * 45 ???
= -51.2 + 51.3 close enough
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