A 5kg block is pulled along a horizontal surface by a 50N force making an angle of 20∘ above the horizontal. The coefficients of friction are μs=0.40 and μk=0.30. Once the block starts moving, its acceleration is
a) 6.4ms−2
b) 4.1ms−2
c) 7.4ms−2
d) 5.5ms−2