Question

3 boys pulling at the end of 3 ropes held together on a knot. one boy pulls with a force of 20 Newton eastward, while a 2nd boy pulls with the same magnitude force northward. in what direction and with what force must a 3rd boy be pulling if his pull of the knot is to be equal and opposite to the combine pulls of the other 2 boys.

Answer 1

The three forces must have a resultant of zero.
The third force must be 20*sqrt2 Newtons, in a SW direction.

Answer 2

40

Answer 3

F1 + F2 = 20N.[0o] * 20N.[90o].
F1+F2 = 20 + 20i = 28.3N.[45o].
F3 must be equal to -(F1+F2).

F3 = -28.3[45o] = 28.3[45+180] = 28.3[225] = 28.3N.[45o] S. of W.