Coefficient of Static Friction between truck and block

[MetallicaFNum]

Homework Statement

An un-tethered block sits on a flatbed truck as it accelerates up an incline that makes an angle of 15° with respect to the horizontal. If the truck speeds up at a rate less than 2.10 m/s2, the block remains on the truck. If the truck speeds up at a rate equal to or greater than this value, however, the block slides off the truck. What is the coefficient of static friction between the truck and the block?

Homework Equations

F = ma
f_s≤µ_s n

The Attempt at a Solution

((9.80 m⁄(s^2)sin(15°) -(2.20 m⁄s^2 ))/((9.80 m⁄s^2 ) cos(15°) )=0.0357

 

[PhanthomJay]

You have a signage error...can you find it? What are the directions of the forces acting on the block, parallel to the incline? What is the direction of its acceleration along the incline?