Acceleration of Slab and Block: 58N Force

[tebes]

Homework Statement

A slab of mass m1 = 18 kg rests on a frictionless floor, and a block of mass m2 = 12 kg rests on top of the slab. Between block and slab, the coefficient of static friction is 0.30, and the coefficient of kinetic friction is 0.20. A horizontal force ,F of magnitude 58 N begins to pull directly on the block. What are the accelerations of (a) the block and (b) the slab?

Homework Equations

The Attempt at a Solution

Attempts for (a)
m1*a= F - fk
Solved for a.
I got it right.

Attempts for (b)
It's sliding (F > Fs) and there is no friction between floor and the slab.
I assumed the fk is pulling the slab. I put it in this way :
m2*a = fk.
Solved for a. But my answer is wrong.

fk = magnitude of kinetic friction between block and slab.
I would guess the equation for my (b) or my assumption is wrong.

 

[PhanthomJay]

Looks right to me. Did you check your math and value for fk?

 

[tebes]

Looks right to me. Did you check your math and value for fk?

I just checked it. It was right. Thank you for checking, phantomjay.