Answer
a. Decrease.
b. Variable.
Work Step by Step
a. It will decrease. Some of the force now is directed upward, so the horizontal component of the force has been decreased. The smaller horizontal force results in a smaller net force and a smaller acceleration.
b. It depends. With friction, the problem requires more analysis. There are two effects that tend to cancel out.
First, consider what happens when you pull slightly upward. The horizontal component of the pulling force becomes smaller, as before. However, the upward component of the pulling force tends to reduce the normal force, which reduces the force of friction: this would increase the acceleration. More math shows that the acceleration increases with pulling angle, up to a point, and then decreases again.
If instead you had pulled slightly downward, the acceleration will decrease no matter what.
