What is the total force exerted by block 2 on block 3 ?

[aruji73]

Four blocks EACH of mass m = 10.0 kg are arranged as shown in the picture, on top of a frictionless table. A hand touching block 1 applies a force of Fh1 = 90.0 N to the right. The coefficient of friction between the blocks is sufficient to keep the blocks from moving with respect to each other.

What is the total force exerted by block 2 on block 3 ?

I got 67.5 N which was wrong

F=90N-22.5=67.5N since a=9/4ms-2

 

[tms]

Start by drawing a free-body diagram showing all the forces. Pay particular attention to blocks 2 and 3, but don't ignore the others.

 

[aruji73]

I now think block 2 would exert a force to block 3 equal to the combined weight of the 2 books above it which is f=2(mg) = 2*10*9.8 = 196 N

but i still get it wrong

 

[tms]

That's part of it, but what about the horizontal direction?

 

[aruji73]

i got it now its sqrt(of horizontal direction ^2 + vertical direction ^2)

 

[tms]

Assuming you are referring to the forces on the block, that is indeed the magnitude of the net force. Now what is the direction?