Coefficient of kinetic friction on wooden plane question

[Daved]

Homework Statement

This is what I was given:
A block is placed on a rough wooden plane it is found that when the plane is tilted 30° to the horizontal, the block will slide down at a constant speed.

Homework Equations

I'm not sure which equations to use other than sinΘmg but I'm not getting the correct answer which is 0.577.

The Attempt at a Solution

I then tried tanΘ and got the correct answer but I'm not sure why it's correct.
Thank you for any help provided.

 

[grzz]

Drawing a FBD is a MUST. This must show all the forces acting on the block.

 

[obafgkmrns]

Try a sanity check: What happens as the plane's tilt approaches 90°? Once you do that, try calculating the friction force.