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Unit 5

5.2 Representations of Changes in Momentum

1 min readβ€’may 31, 2020

Kanya Shah


Two Object Problems

When you’re given a two object problem and you’re asked to calculate the change in momentum, take into account the initial momentum and the final momentum individually first of each object. pinitial = pfinal. When you solve for the final momentum, decide whether you should use an individual mass value or the sum of all masses in the system.
If you’re solving for the final velocity of the system, then you should absolutely use the sum of both masses regardless of how many objects there are. If an object is initially at rest, it’s initial momentum will be zero since its velocity in the beginning was zero (p = m*v).Β 
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fph.PNG?alt=media&token=267dc7f9-c55a-4947-a2e3-ee2381051e28
Change in momentum is proportional to the force and time so if you decrease T or F, you decrease the change in momentum.

Image Credit: ponderisd.net

Interpreting Different Scenarios

You need to be able to interpret different scenarios, especially with problems that have multiple external forces acting on the system. When you see problems like that, make sure you find the vector sum of the forces after calculating individual forces. If you’re looking for the momentum, you can either find individual momentums of the objects or find the total momentum of the system. Understand how to apply the formula and make sure you can explain your thought process because some FRQ’s ask for conceptual explanations.Β 
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Ff.PNG?alt=media&token=5a2cf595-2910-4a90-adff-9b68d850d75b

Image Credit: studyblue.com

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