-45.0 kg girl is standing on a 161 kg plank. The plank, originally at rest, is free to slide on a frozen lak rictionless surface. The girl begins to walk along the plank at a constant velocity of 1.46 m/s relative to lirection the girl is moving in be positive. Indicate the direction with the sign of your answer.) (a) What is her velocity relative to the surface of ice?

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A 45.0 kg girl is standing on a 161 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 1.46 m/s relative to the plank. (Let the
direction the girl is moving in be positive. Indicate the direction with the sign of your answer.)
(a) What is her velocity relative to the surface of ice?
m/s
(b) What is the velocity of the plank relative to the surface of ice?
m/s
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Transcribed Image Text:A 45.0 kg girl is standing on a 161 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 1.46 m/s relative to the plank. (Let the direction the girl is moving in be positive. Indicate the direction with the sign of your answer.) (a) What is her velocity relative to the surface of ice? m/s (b) What is the velocity of the plank relative to the surface of ice? m/s Need Help? Read It
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Step 1

Given: The mass of the girl is 45.0 kg.

           The mass of the plank is 161 kg.

           The initial velocity of the girl with respect to the plank is 1.46 m/s.

To determine: (a) Velocity of the girl relative to the surface of ice.

It is given that plank is originally at rest so initial velocity of the plank is zero, vpi=0

Let the initial velocity of the girl be vgi.

Th velocity of the girl with respect to plank is vgp=1.46 m/s

The equation for velocity is 

vgi=vgp+vpi ................................................ (1) 

where vgi is the velocity of the girl relative to ice, vgp is the velocity of girl relative to plank and vpi is the velocity of plank relative to ice. 

The momentum is conserved for this girl-plank system. Initial momentum of the system is equal to final momentum. 

mgvgi+mpvpiInitial=mgvgi+mpvpifinal ............................................ (2) 

where mg and mp are the mass of the girl and the plank respectively. 

The girl is initially is standing on a plank and the plank is at rest, so the initial velocity of the girl and the plank are zero. 

mg×0+mp×0Initial=mgvgi+mpvpifinal0=mgvgi+mpvpifinal

 

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