Two children push on opposite sides of a door during play. Both push horizontally and perpendicular to the door. One child pushes with a force of 17.5 N at a distance of 0.600 m from the hinges, and the second child pushes at a distance of 0.450 m. What force must the second child exert to keep the door from moving? Assume friction is negligible.

The second child must exert a force of magnitude 23.3N to keep the door from moving.

Explanation:

We have to find the moment that the first child exerts and then match it to that exercised by the second child.

F1 = 17.5N

d1 = 0.6m

F2=?

d2 = 0.45m

M = F * d

M1 = 17.5N * 0.6m

M1 = 10.5 N. m

M1=M2

M2 = F2 * 0.45m

10.5 N. m = F2 * 0.45m

10.5 N. m/0.45m = F2

F2=23.3 N