#Falling blocks on a string physics 100n pull at it free
The free body diagrams showing only the horizontal forces for the three masses and the two strings (each regarded as a separate system) are shewn below.įorces a and b (force on mass $m_3$ due to left hand string and force on left hand string due to mass $m_3$), c and d, e and f, g and h are all Nweton's third law pairs (equal in magnitude and opposite in direction.įorces b and c, f and g represent the forces on the two strings which, the the strings are assumed massless, are equal in magnitude and opposite in direction so the net force on each string is zero.īecause the strings are also assumed to be inextensible the acceleration of each of the masses must be the same. If you are going to use Newton's second law then first define the system you are considering and then draw the appropriate free body diagram. The forces shown on your diagram might well be there to help you but also thay seem to have confused you. Free body diagrams for the three blocks would help greatly. What's with the direction of $T_1$ and $T_2$ given in the diagram? The first time I did this question I actually made a silly mistake and considered a force that wasn't acting on the second block, but was in fact being applied by the second block (tension $T_2$ in the right direction). I'm really confused as to what forces are acting on the second block, and in which direction. The problem arises when I get to the second block. So my first equation is $F - T_2 = m_1a$. The forces on $m_1$ are $F = 40 N$ in the right direction and tension $T_2$ in the left. I got to a system of equations, but I feel I missed something. Three blocks of masses $m_1$, $m_2$ and $m_3$ are connected to a massless string on a frictionless table as shown in the figure. This was a problem in an examination paper that I was solving:
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