Aboy flies a kite with the string at a 30 degree angle to the horizontal. the tension in the string is 4.5n .

how much work in j does the string do on the boy if the boy stands still?

how much work does the string do on the boy if the boy walks a horizontal distance of 11m away from the kite?

how much work does the string do on the boy if the boy walks a horizontal distance of 11m toward the kite

How much work in J does the string do on the boy if the boy stands still? 

None. The equation for work is W = force x distance. Since the boy isn't moving, the distance is zero. Anything times zero is zero 
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How much work does the string do on the boy if the boy walks a horizontal distance of 11m away from the kite? 

might be a trick question since his direction away from the kite and his velocity weren't noted. Perhaps he just set the string down and walked away 11m from the kite. If he did this, it is the same as the first one...no work was done by the sting on the boy. 

If he did walk backwards with no velocity indicated, and held the string and it stayed at 30 deg the answer would be: 
4.5N + (boys negative acceleration * mass) = total force1 
work = total force1 x 11 meters 
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How much work does the string do on the boy if the boy walks a horizontal distance of 11m toward the kite? 

same as above only reversed: 
4.5N - (boys negative acceleration * mass) = total force2 
work = total force2 x 11 meters

Iwould sure like to answer your question but i honestly just don’t know

Ibelieve that the correct answer is: c. along plate boundaries