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**conservation of momentum??**

## Homework Statement

A 45.0 kg girl is standing on a 156 kg plank. The plank, originally at rest, is free to slide on a frozen lake, which is a flat, frictionless surface. The girl begins to walk along the plank at a constant velocity of 1.51 m/s relative to the plank.

(a) What is her velocity relative to the ice surface?

(b) What is the velocity of the plank relative to the ice surface?

variable:

girl=45kg

plank=156kg

Vi=0m/s

Vf=1.51m/s

## Homework Equations

mavai + mbvbi = mavaf +mbvbf

## The Attempt at a Solution

since Vi=0m/s left side of consercation of momentum equation =0

0 = 45(Vf) + 156(1.51)

0 = 45(Vf) + 235.56

-235.56 = 45(Vf)

-5.23 = Vf

this answer is not possible because the absolute value of part a and b should add up to 1.51 while 5.23 is already much bigger