Basic Newtons Laws problem

Question

Force F is applied to the front block (as shown below) in order for all three blocks to move at a constant velocity. All horizontal surfaces have a coefficient of friction of µ. What is the ratio of force F to the block of mass 2m exerts on the block to it's left?

[block mass m]

Force F -----> [block mass m][block mass 2m]

----------------------------------------------------------------------

Ground

Answer 1

Treat the masses as one big mass and find acceleration. Then use the second law to find the Force exerted by the second block on the 1st block. Then calculate ratio:

(m+2m)a = F - mgμ-2mgμ solve for a of both masses in terms of F and m

ma = F - mgμ - F_{Blk2 on Blk1} substitute in a from above and solve for the Force of Block 2 on 1