3.A force of 26lbs. causes impending motion. If the force is maintained at 26lbs.Fn=Fw=65lbs and the sliding friction is .28.

find:
a.mass of the block
b.FF
c.acceleration
What force must be maintained to cause an acceleration of 2ft/s^2?

<<and the sliding friction is .28.

>>
You need to be more precise defining the problem. Do you mean the coefficient of sliding friction is 0.28? What does FF stand for?

a) If the surface is level, Fn = Fw is the weight. The mass is Fn = Fn/g. g = 32.2 ft/s^2 and the mass will be in slugs.
b) The friction force (FF?) is (0.28) x (weight)
c) acceleration = (Applied force - Friction force) / mass

Use F = ma to get the net force required for a = 2 ft/s^2.