A 4kg block is held against a vertical wall by a constant horizontal force of 100N. The coefficients of friction between the block and the wall are μs=0.5 and μk=0.3. The block is given a brief downward push so that it starts sliding downward. The magnitude of its acceleration during the slide is
a) 9.8m/s2 downward
b) 2.3m/s2 downward
c) 0.94m/s2 downward
d) 2.7m/s2 upward