This was a problem in an examination paper that I was solving:
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. They are pulled with a force $F = 40 N$ . If $m_1 = 10 kg$ , $m_2 = 6 kg$ , and $m_3 = 4 kg$ , then tension $T_2$ will be
(a) $10 N$
(b) $20 N$
(c) $32 N$
(d) $40 N$
I got to a system of equations, but I feel I missed something. The forces on $m_1$ are $F = 40 N$ in the right direction and tension $T_2$ in the left. The system is, of course, accelerating. So my first equation is $F - T_2 = m_1a$ .
The problem arises when I get to the second block. I'm really confused as to what forces are acting on the second block, and in which direction. I feel that is where I went wrong. 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). The diagram doesn't help much either. What's with the direction of $T_1$ and $T_2$ given in the diagram?
I need a little help here. Free body diagrams for the three blocks would help greatly.