Impulse/final velocity question confusion

AI Thread Summary
The discussion revolves around a confusion regarding momentum calculations in a physics problem. The user questions the transition from 50 kgm/s to 30 kgm/s in the equation, suggesting it should be 70 kgm/s instead. Clarification is provided that north is considered positive, making south negative, which affects the signs in the equation. The correct interpretation of subtracting a negative value resolves the confusion, confirming that the calculations align with the physics principles. Ultimately, the misunderstanding was clarified through careful attention to the signs in the equation.
student07
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I uploaded my question below; basically I am confused in part b) where they show that:
50 kgm/s = (5kg)v2 - (5kg)(-4m/s) then they say that
30 kgm/s = 5kg v2, but shouldn't it be 70 kgm/s = 5kg v2?

As noted at the beginning of the question North is positive and thus since the cart moves south is negative (-4m/s).
Could this be a typo ?
 

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If south is negative and that was the initial direction of momentum then the second term is written correctly. Note carefully the signs (subtracting a negative on the RHS) so the second line is correct because the equation reads (without units) 50 = 5v + 20.
 
yeah I totally missed the subtracting a negative on the RHS that makes more sense now thank you
 

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