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## Homework Statement

The horizontal surface on which the objects slide is frictionless. The acceleration of gravity is 9.8 m/s2. Three blocks are sliding on a frictionless horizontal surface:

Fℓ----->[Block1-1kg][Block2-7kg][Block3-4kg]<--Fr

If Fℓ = 29 N and Fr = 3 N, what is the magnitude of the force exerted on the block with mass 7 kg by the block with mass 4 kg?

## Homework Equations

F = ma

## The Attempt at a Solution

29 N - 3 N = 26 N (total force) 1kg + 7 kg + 4 kg = 12 kg (total mass)

a= F/m = 26 N/12 kg = 2.166666667 m/s2 (acceleration of all the blocks in the right direction)

masses of Block2 + Block 3 = 11 kg

F = (11 kg)(2.166666667) = 23.83333333 N (THIS IS THE WRONG ANSWER!)

What am I doing wrong?