$($a$)$ Did the child move to the left or to the with the result that the force exerted by the father is reduced from $0\mathrm{.}75$ mg to $0\mathrm{.}60$ mg $.$ ment. $[$Answer: $($a$)$ The child moved to thght$?$ Explain. $($b$)$ Determine the distance and direction of the child's displacement

Answer the practice problem based on the photo

EXAMPLE $11-7$ FIND THE FORCES: AXIS ON THE RIGHT

A child of mass $m$ is supported on a light plank by his parents, who exert the forces $F_1$ and $F_2$ as indicated in the sketch. Find the forces required to keep the plank in static equilibrium. $$se the right end of the plank as the axis of rotation.

PICTURE THE PROBLEM

Our sketch shows the same physical system as in Figure $11-10,$ only this time the axis of rotation is at the right end of the plank.

REASONING AND STRATEGY

We set both the net force and the net tor equal to zero. The expression for the net torque is different this time, due to the new location for the axis of rotation, but the final result for the forces will be the same.

Known Mass of child, $m$; distance for force $1,L$; distance for force $2,0$ ; distance for weight $($ mg $)$ of child, $\frac{L}{4}.$

Unknown $,F_1=F_2=?$

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