Chapter 7. External force and total momentum change for a system of objects (7-13)

Question

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{"title":"The sum of all external forces acting on a system of objects","description":"Correct!","type":"correct","color":"#99CCFF","code":"[{\"shape\":\"poly\",\"coords\":\"82,133\"},{\"shape\":\"rect\",\"coords\":\"42,18,150,39\"}]"} {"title":"Duration of a time interval over which the external forces act","description":"Wrong","type":"incorrect","color":"#ffcc00","code":"[{\"shape\":\"rect\",\"coords\":\"160,9,183,37\"},{\"shape\":\"rect\",\"coords\":\"118,11,119,13\"}]"} {"title":"Change during that time interval in the total momentum of the objects that make up the system","description":"Incorrect","type":"incorrect","color":"#333300","code":"[{\"shape\":\"poly\",\"coords\":\"113,132\"},{\"shape\":\"rect\",\"coords\":\"274,9,300,38\"},{\"shape\":\"rect\",\"coords\":\"220,18,238,34\"}]"}

Question

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{"title":"The sum of all external forces acting on a system of objects","description":"Wrong","type":"incorrect","color":"#99CCFF","code":"[{\"shape\":\"poly\",\"coords\":\"82,133\"},{\"shape\":\"rect\",\"coords\":\"42,18,150,39\"}]"} {"title":"Duration of a time interval over which the external forces act","description":"Correct!","type":"correct","color":"#ffcc00","code":"[{\"shape\":\"rect\",\"coords\":\"160,9,183,37\"},{\"shape\":\"rect\",\"coords\":\"118,11,119,13\"}]"} {"title":"Change during that time interval in the total momentum of the objects that make up the system","description":"Incorrect","type":"incorrect","color":"#333300","code":"[{\"shape\":\"poly\",\"coords\":\"113,132\"},{\"shape\":\"rect\",\"coords\":\"274,9,300,38\"},{\"shape\":\"rect\",\"coords\":\"220,18,238,34\"}]"}

Question

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{"title":"The sum of all external forces acting on a system of objects","description":"Wrong","type":"incorrect","color":"#99CCFF","code":"[{\"shape\":\"poly\",\"coords\":\"82,133\"},{\"shape\":\"rect\",\"coords\":\"42,18,150,39\"}]"} {"title":"Duration of a time interval over which the external forces act","description":"Incorrect","type":"incorrect","color":"#ffcc00","code":"[{\"shape\":\"rect\",\"coords\":\"160,9,183,37\"},{\"shape\":\"rect\",\"coords\":\"118,11,119,13\"}]"} {"title":"Change during that time interval in the total momentum of the objects that make up the system","description":"Correct!","type":"correct","color":"#333300","code":"[{\"shape\":\"poly\",\"coords\":\"113,132\"},{\"shape\":\"rect\",\"coords\":\"274,9,300,38\"},{\"shape\":\"rect\",\"coords\":\"220,18,238,34\"}]"}

Review

The quantity in parentheses on the left-hand side of Equation 7-12 is the sum of all of the \(\textit{external forces}\) that act on the \(\textit{system}\) of objects A and B. We’ll call this \(\sum{\vec{F}_\mathrm{external\ on\ system}}\) for short. The right-hand side of the equation is the difference between the total momentum of the system after the time interval \(\Delta{t}\), \(\vec{P}_f = \vec{p}_{Af} + \vec{p}_{Bf}\), and the total momentum of the system before the time interval, \(\vec{P}_i = \vec{p}_{Ai} + \vec{p}_{Bi}\). So we can rewrite Equation 7-12 as: