Determine the magnitude of the force exerted on the block

[EG78362]

Homework Statement

Given: The surface is frictionless, two blocks in contact with each other move to the right across a horizontal surface.
Note: one block is 2.1kg with a 58N force applied to it, and the other block is 5.7kg with a 13N force applied to it.

Homework Equations

Determine the magnitude of the force exerted on the block with mass 2.1kg by the block with mass 5.7 kg

The Attempt at a Solution

First I subtracted 58N-13N=45 to get the net force, then I divided the net force by the mass of both blocks [45N/7.8kg]=5.769m/s^2 to get acceleration.
Then I multiplied the acceleration by the 2.1kg block to get 12.115N, but this was not the right answer. So thinking that I maybe did it wrong I multiplied the acceleration by the 5.7kg block (32.884N)and this was also incorrect, finally not knowing what I was doing wrong still, I subtracted 32.884-12.115 and of course this was wrong as well. I can't figure out what I'm missing here. Any help would be appreciated.

 

[cepheid]

Assumption I'm going to make: 2.1 kg block is on the left, pushed on with force 58 N from the left side, in the right direction. 5.7 kg block is on the right, pushed on with force 13 N from the right side, in the left direction.

Envisioning a FBD for the first block, if it's only moving with the acceleration you calculated to the right, then the net force on it must be 12.115 N (assuming you calculated that right) to the right, which means that there must be a force of magnitude 58 N - 12.115 N on it to the left, counteracting the 58 N force to the right partially. So, is 45.885 N the correct answer?

 

[EG78362]

Okay, I was thinking I had to subtract from the net force. Thank you so much, I got it right this time.

 

[cepheid]

Okay, I was thinking I had to subtract from the net force. Thank you so much, I got it right this time.

No problem! Always draw a free body diagram to check your thinking.