Kinetic friction find greatest acceleration

[Sneaky07]

1. A crate resting on a rough horizontal floor is to be moved horizontally. The coefficient of kinetic friction is 0.40. To start the crate moving with the least possible applied force, in what direction should the force be applied?

a. Horizontal

b. 24 degrees below horizontal

c. 22 degrees above the horizontal

d. 24 degrees above the horizontal

e. 66 degrees below the horizontalFormulas I used.
2. (Normal force) Fn = m*a
(Kinetic frictional force) Fk = (uk)*|Fn| (uk being coefficient of kinetic friction)

Work I did.
3. Figured out the normal force which was m*a*cos(theta). After I multiplied it by the (uk) and got kinetic frictional force but don't know where to go from there...

Thanks in advance!

 

[tiny-tim]

Welcome to PF!

1. A crate resting on a rough horizontal floor is to be moved horizontally. The coefficient of kinetic friction is 0.40. To start the crate moving with the least possible applied force, in what direction should the force be applied?
…
Figured out the normal force which was m*a*cos(theta). After I multiplied it by the (uk) and got kinetic frictional force but don't know where to go from there...

Thanks in advance!

Hi Sneaky07! Welcome to PF!

(have a theta: θ and a mu: µ )

However did you get m*a*cos(theta)?

Hint: this is a straightforward Newton's second law problem …

call the force "F", then take vertical components and horizontal components (separately), to get two equations for F.