I'm having trouble with question #9

 

for a it's just a simple normal force question with a block on an angle. So I did the usual mgcos(angle) = F_normal and it didn't work.

 

for b I used F_hor - mgsin(angle) = ma, solved for the acceleration and it also didn't work.

 

I'm I missing something here?

 

 

 

Don't forget, in this problem there's also a force pushing the block up the incline.  So your equation to find F_N would look more like:

 

Ok thanks!