A boy 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

From our physics class, we know that Work is a product of Force and Displacement. The force must be the force in the same direction with the displacement. So force and displacement must be parallel.

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

Since we know that: Work = Force * Displacement

and in this case displacement is equal to zero, therefore Work must also be equal to zero.

Work = 0

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

Now are given a displacement of 11 m which is a horizontal distance. Therefore we must first calculate the horizontal component of force:

Fx = 4.5 N * cos 30

Fx = 3.897 N

So work is:

Work = 3.897 N * 11 m

Work = 42.87 J ~ 43 J