Three people pull simultaneously on a stubborn donkey. jack pulls directly ahead of the donkey with a force of 97.9 n, jill pulls with 72.7 n in a direction 45â° to the left, and jane pulls in a direction 45â° to the right with 145 n. (since the donkey is involved with such uncoordinated people, who can blame it for being stubborn? ) find the magnitude of the net force the people exert on the donkey.

We should analyze the forces in two different directions: the forward-backward direction and the left-right direction, and then calculate the resultant of the net forces acting on both directions.

Forward-backward direction. Here we have three forces acting on the monkey: the force applied by Jack, 97.9 N directly ahead; the force applied by Jill, 72.7 N with an angle  to the left; and the force applied by Jane, 145 N with an angle . Therefore, the resultant on this axis is


Left-right direction. In this direction, the force applied by Jack is 0 N, because he is applying his force only ahead. The force applied by Jill is 72.7 N with an angle  to the left, while the force applied by Jane is 145 N with an angle  to the right: this means we should write the two forces with opposite signs, because they have opposite direction in the left-right axis. Therefore,


The net force acting on the monkey is the resultant of these two forces: