Momentum Relative to Surface / Plug-and-Chug

AI Thread Summary
The discussion revolves around a physics problem involving momentum conservation as Stevie walks on a rolling platform. The key equations used include the conservation of momentum to establish the velocities of both Stevie and the platform relative to the floor. The initial confusion stemmed from determining the correct reference point for the calculations. Ultimately, the correct velocities were found to be -0.43 m/s for the platform and 0.77 m/s for Stevie. The importance of considering the platform's mass while calculating the system's momentum was highlighted.
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Homework Statement



Stevie stands on a rolling platform designed for moving heavy objects. The platform has mass of 76 kg and is on a flat floor, supported by rolling wheels that can be considered to be frictionless. Stevie's mass is 43 kg. The platform and Stevie are stationary when she begins walking at a constant velocity of +1.2 m/s relative to the platform. (a) What is the platform's velocity relative to the floor? (b) What is Stevie's velocity relative to the floor?

Homework Equations



(p)i = (p)f Conservation of Momentum


The Attempt at a Solution



Used Conservation of Momentum, but I am having trouble establishing a reference point.

43x1.2 + 76xV2f = 0 - That's for the the platform and Stevie.

.521x119 = 43xV1f + 76xV2f - That's for the entire system...I think.

As stated above, I think my problem is finding the reference point. I would normally spend more time with this one by myself, but I have a quiz on this fairly soon.


The answers:
(a) −0.43 m/s
(b) 0.77 m/s
 
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Your first equation would give you the correct answer if you considered that the platform has additional mass as a result of someone standing on it.
 
Of course it would.

You're the man BishopUser. Thanks dude.
 

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