A man pulls a child a distance in a wagon of mass m along a horizontal sidewalk

Question

A man pulls a child a distance in a wagon of mass m along a horizontal sidewalk with a constant velocity v. The coefficient of friction on of the sidewalk is mu. The forces on the child are: the force of gravity (mg); the sidewalk's vertical force upward (F_n); the force of friction (Ff); and the force applied by the man (F_f). If the man does 100 J of work in this process, the work done by F_a the vertical force upward from the sidewalk (including the sign), is +100 J. is -100 J. is zero. can't be determined without knowing mu and m. can't be determined without knowing m and v.

Explanation / Answer

FN is acting upward
displacement is in horizontal direction
work = F*d* cos thetha
here thetha is 90 degree
cos thetha will be 0
so,
work = F*d* cos thetha
= 0

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