Solve Sliding Box Problem: Force Normal, Constant Velocity & Acceleration

[KatieLynn]

Homework Statement

A student is pulling a 25 kg trunk up an incline that has an angle with the horizontal of 20 degrees. She has a strap tied to the trunk which is parallel to the surface of the incline. If the coefficient of kinetic friction between the incline and the trunk is 0.5 fine
a)Force Normal
b) the force necessary to keep the trunk moving at a constant velocity.
c)the force she would have to apply to accelerate the trunk up the incline at 0.5 m/s squared.

Homework Equations

f(net)=ma
coeff.=(force friction)/(force normal)

The Attempt at a Solution

So I think I found (A) to be force normal = 230N by doing Fn=(m)(g)(cos20)
I tried doing this for B (25)(-9.81)(sin20)-(0.5)(25)(-9.81)(cos20) + ForceX =0
I got 31 but that's not right...

 

[Astronuc]

(25)(-9.81)(sin20) + (0.5)(25)(-9.81)(cos20) + ForceX = 0

The friction force opposes motion, so it must point down the ramp, and the weight component parallel to the ramp must also point down the ramp. So these two force must have the same sign (direction). Both oppose the pulling force up the ramp.