Block on a Wedge: Solving the 0N Equation

[zohapmkoftid]

Homework Statement

http://uploadpie.com/7kzGG

Homework Equations

The Attempt at a Solution

The correct answer is A : 0N
But my answer is B : 12 N
Here is my attempt

http://uploadpie.com/UUGwM

I know I can consider the block and the wedge as one system and I can get the correct answer. But I want to know what's wrong with this approach.
Thanks for help

 

[tiny-tim]

Welcome to PF!

Hi zohapmkoftid! Welcome to PF!

I know I can consider the block and the wedge as one system and I can get the correct answer. But I want to know what's wrong with this approach.

Yes, Rsinθ is the horizontal component of the normal component of the reaction force

But you haven't included the whole reaction force …

what about the friction component? ​

 

[zohapmkoftid]

Yes, I haven't considered f cos
thank you!