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[SOLVED] Newton's Third Law problem
Three boxes, A, B, and C, are positioned next to each other on a horizontal, frictionless surface. An applied force acting on box A causes all the boxes to accelerate at 1.5m/s^{2}
Homework Statement
Three boxes, A, B, and C, are positioned next to each other on a horizontal, frictionless surface. An applied force acting on box A causes all the boxes to accelerate at 1.5m/s^{2}
. Calculate the force that box B exerts on box A.
F_{A on B}= -F_{B on A}
F=ma
What seems to be the issue is how my teacher solved this problem. I have only realized this problem, so I can't have asked her personally. What she did is isolate box B and find the F_{net} acting on it. This is the calculation she did:
F_{net}= F_{A on B}-F_{C on B}
F_{net}= m_{B}a -(-7.5 N)
F_{net}= (10 Kg)(1.5m/s^{2}) + 7.5 N
F_{net}= 23 N
However, what confused me is the two negative signs she put infront of the 7.5 N. I think only one would suffice to take into consideration that F_{C on B} is a negative value, being that its direction is left.
I solved this problem taking a different approach. I found F_{net} of box B and C, and added them together. Here are my calculations:
F_{net}= m_{B}a + m_{C}a
F_{net}= (10 Kg)(1.5m/s^{2}) + (5.0 Kg)(1.5m/s^{2})
F_{net}= 23 N
Could someone please confirm whether my method of solving the problem is correct or not?
http://img70.imageshack.us/img70/8836/thirdlaw2cf8.png
[/URL]Homework Equations
F_{A on B}= -F_{B on A}
F=ma
The Attempt at a Solution
What seems to be the issue is how my teacher solved this problem. I have only realized this problem, so I can't have asked her personally. What she did is isolate box B and find the F_{net} acting on it. This is the calculation she did:
F_{net}= F_{A on B}-F_{C on B}
F_{net}= m_{B}a -(-7.5 N)
F_{net}= (10 Kg)(1.5m/s^{2}) + 7.5 N
F_{net}= 23 N
However, what confused me is the two negative signs she put infront of the 7.5 N. I think only one would suffice to take into consideration that F_{C on B} is a negative value, being that its direction is left.
I solved this problem taking a different approach. I found F_{net} of box B and C, and added them together. Here are my calculations:
F_{net}= m_{B}a + m_{C}a
F_{net}= (10 Kg)(1.5m/s^{2}) + (5.0 Kg)(1.5m/s^{2})
F_{net}= 23 N
Could someone please confirm whether my method of solving the problem is correct or not?
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