Question

Three blocks 1, 2, & 3 rest on a horizontal frictionless surface, as shown. Each block has a mass m and the blocks are connected by massless strings. Block 3 is pulled to the right by a force F. The resultant force on block 2 is:

• A. Zero
• B. (1/3)F
• C. (1/2)F
• D. (2/3)F

Answer 1

The correct option is B (1/3)F

According to the constraint of the system, all the three blocks will move with the same acceleration given by,
$a=F/(3\ast m)$
Now, net force on second block will be equal to it's mass times acceleration.
$F_{eq2}=m\ast a=m\ast \left(F/3m\right)$
$F_{eq2}=F/3$