- #1
Peter J
- 7
- 0
moved from general physics forum
Hello guys , i am really confused about this problem
when i construct the free body diagram for each object individually , every thing goes fine and i can solve the problem and get the right solution,
BUT , as our professor said , we can consider two or more object as one system and apply Newtons law on it IF THEY HAVE THE SAME ACCELERATION , in this problem both have same acc , which is (0) .
but when i consider them is a system :
sum of external forces = m(total).a : a=0 >
sum of external forces=0 >
F-f (friction) =0
F=f(friction)
F=0.30 * 6.1 N = 1.83N Which is wrong ! the right answer is 3 N
-------
up to know , every problem that involved 2 or more objects with same acceleration i was able to solve it either way (consider all of them as a system and analyse the external forces , or by dividing them and study each object alone )
but this one does not seem to work for me .
-------
is there any thing wrong with eliminating the tension T from the equation of the composed system because it is an internal force ?
is there any thing wrong with eleminating the friction (A on B ) , ( B on A ) T from the equation of the composed system because it is an internal force ?
whats wrong !?
Thanks
when i construct the free body diagram for each object individually , every thing goes fine and i can solve the problem and get the right solution,
BUT , as our professor said , we can consider two or more object as one system and apply Newtons law on it IF THEY HAVE THE SAME ACCELERATION , in this problem both have same acc , which is (0) .
but when i consider them is a system :
sum of external forces = m(total).a : a=0 >
sum of external forces=0 >
F-f (friction) =0
F=f(friction)
F=0.30 * 6.1 N = 1.83N Which is wrong ! the right answer is 3 N
-------
up to know , every problem that involved 2 or more objects with same acceleration i was able to solve it either way (consider all of them as a system and analyse the external forces , or by dividing them and study each object alone )
but this one does not seem to work for me .
-------
is there any thing wrong with eliminating the tension T from the equation of the composed system because it is an internal force ?
is there any thing wrong with eleminating the friction (A on B ) , ( B on A ) T from the equation of the composed system because it is an internal force ?
whats wrong !?
Thanks