Finding maximum velocity?

[shock7221]

finding maximum velocity??

A block of mass M = 275.0 g sits on a horizontal tabletop. The coefficients of static and kinetic friction are 0.54 and 0.38, respectively, at the contact surface between table and block. The block is pushed on with a 12.0 N external force at an angle θ below the horizontal.
(a) What angle will lead to the maximum acceleration of the block for a given pushing force?
20.8° above the horizontal

(b) What is the maximum acceleration?
43 m/s^2

those were the answer given. I know how you get the degrees but i am having trouble how to find the maximum acceleration... can you guy help me?

 

[gneill]

Well, if you managed to find the angle, you should have no trouble plugging it into the equation you found for the maximum acceleration...

 

[shock7221]

well i did. a=(sin20.8)(9.8)(12)= 41.7 m/s^2.. its close but it is not the right answer.

 

[gneill]

Perhaps you should start with a free body diagram of the forces, and determine the net horizontal force acting. Newton's second law then provided the acceleration.