Movement at constant velocity means that the applied force and friction are balanced (equal, opposite forces)
a) Applied force = friction force = fric.coef. x weight(normal force) ..
F = 0.35 x (50kg x 9.8N/kg) .. .. ?F = 171.5 N

b) Work done by applied force, + W .. and work done by friction - W (in opposite direction) are equal at constant speed .. net work done = 0 J

c) Work done by applied force = F x distance = 171.5 N x 5.0 m .. .. ?W = (+) 857.5 J
Work done by friction .. ?=(-) 857.5 N

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