Find x, where shear = 0 and bending = maximum:
Vbr-w2 x = 0; x = Vbr/w2 = 2000/200 x = 10 ft
Note: stress is figured, using absolute maximum bending and shear, regardless if positive or negative. Lumber sizes are nominal, yet actual sizes are used for computation. Actual sizes are ½ in. less for lumber up to 6 in. nominal and ¾ in. less for larger sizes: 4x8 nominal is 3½x7¼ in. actual.
Note: in the above two beams shear stress is more critical (closer to the allowable stress) than bending stress, because negative cantilever moments partly reduces positive moments.