Impulse/final velocity question confusion

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SUMMARY

The discussion centers on a confusion regarding the calculation of final velocity in a momentum problem involving a 50 kgm/s momentum equation. The equation presented is 50 kgm/s = (5kg)v2 - (5kg)(-4m/s), leading to the conclusion that 30 kgm/s = 5kg v2. The participant initially questioned whether the correct equation should be 70 kgm/s = 5kg v2, but clarified that the signs in the equation were correctly applied, particularly noting the importance of subtracting a negative value. This understanding resolved the confusion regarding the momentum direction and calculations.

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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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