A girl of mass mg is standing on a plank of mass mp. Both are originally at rest on a frozen lake that constitutes a frictionless, flat surface. The girl begins to walk along the plank at a constant velocity VGP to the right relative to the plank. (The subscript GP denotes the girl relative to the plank.)

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Chapter9: Linear Momentum And Collisions
Section: Chapter Questions
Problem 66P: Two particles of masses m1 and m2 , move uniformly in different circles of radii R1 and R2 R2 about...
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A girl of mass mG İs standing on a plank of mass mp.
Both are originally at rest on a frozen lake that
constitutes a frictionless, flat surface. The girl begins
to walk along the plank at a constant velocity VGP to
the right relative to the plank. (The subscript GP
denotes the girl relative to the plank.)
(a) What is the velocity vp, of the plank relative to
the surface of the ice? (Use the following as
necessary: VGP, MG, and mp. Indicate the direction
with the sign of your answer. Let the positive
direction be in the direction that the girl walks.)
MGVGP
mg+m,
(b) What is the girl's velocity vGI relative to the ice
surface? (Use the following as necessary: VGp, mG
and mp. Indicate the direction with the sign of your
answer. Let the positive direction be in the
direction that the girl walks.)
(m,VGp)
mg+m,
Transcribed Image Text:A girl of mass mG İs standing on a plank of mass mp. Both are originally at rest on a frozen lake that constitutes a frictionless, flat surface. The girl begins to walk along the plank at a constant velocity VGP to the right relative to the plank. (The subscript GP denotes the girl relative to the plank.) (a) What is the velocity vp, of the plank relative to the surface of the ice? (Use the following as necessary: VGP, MG, and mp. Indicate the direction with the sign of your answer. Let the positive direction be in the direction that the girl walks.) MGVGP mg+m, (b) What is the girl's velocity vGI relative to the ice surface? (Use the following as necessary: VGp, mG and mp. Indicate the direction with the sign of your answer. Let the positive direction be in the direction that the girl walks.) (m,VGp) mg+m,
Expert Solution
Part (a)

The girl plank system is isolated, so horizontal momentum is conserved.

 

The expression for the law of conservation of momentum relative to the ice,

pgi+ppi=pgf+ppf

 

The motion is in one dimension,

vgii^=vgpi^+vpii^vgi=vgp+vpi

Step 2

Rewrite the expression for equation (1) relative to momentum,

mgvgii^+mpvpii^=0mgvgi+mpvpi=0

 

Substitute,

mgvgp+vpi+mpvpi=0mgvgp+mgvpi+mpvpi=0mgvgp=-vpimg+mpvpi=-(mgmg+mp)vgp

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