The Physics of Frictionless Blocks

[EricSomin]

Homework Statement

Blocks with masses of 2kg , 4kg , and 6kg are lined up in a row on a frictionless table. All three are pushed forward by a 60 force applied to the 2 block.

how much force does the 4kg block exert on the 6kg block?

how much force does the 4kg block exert on the 2kg block?

Homework Equations

Newtons Laws. and sum of forces.

The Attempt at a Solution

now i understand Newtons laws of action and reaction. so I am assuming the amount of force acting on the 2kg block from the 4kg block is the same as the 4kg block from the 2kg block.
(wouldnt this mean the system is in equilibrium though?)

anyway, I am confused by how to approach this problem. there is no friction, so wouldn't any force at all cause these blocks to start moving?

if there is no friction, why would the force exerted on the 4kg block from the 2kg block be any different than the force exerted directly onto the 2kg block (60.0N)...wouldnt any force cause the system to accelerate since there is no friction to overcome...

i understand conceptually that m(g) is the force of gravity acting on the block in N. but how would that translate into the loss of force between the blocks of different mass...?im rambling mostly because I am lost with this, how should i begin to approach this problem?

any help at all is greatly appreciated.

 

[1MileCrash]

Try drawing a free body diagram of each block, and marking all forces on each block.

 

[EricSomin]

Try drawing a free body diagram of each block, and marking all forces on each block.

okay, so i see that for the 2kg block and the 4kg block there is a 3rd law pair. (F of 4 acting on 2) so this will become an internal force

also there is the force from 6kg to 4kg and a force from the 4kg on the 6kg. this is also a 3rd law pair. so i will make it an internal force...

i now have the normal force, and F_G for each block, as well as the pushing force (60.0N) on my 2kg block.

would i start by summing the forces in the X direction...if i did that though i would have only 1 force, (force of the push) assuming 3rd law pairs cancel each other out of the problem...im guessing i must find a way to make the F_G have an effect on the pushing force. but one is in the y direction. and the other is in the x. so how would i make these affect each other...

 

[Doc Al]

im guessing i must find a way to make the F_G have an effect on the pushing force. but one is in the y direction. and the other is in the x. so how would i make these affect each other...

Treat the x and y directions separately. You can safely assume that there's no acceleration in the y direction.