Problems

$3\mathrm{.}19$ Two $60-N$ forces are applied as shown to the corners A and $C$ of a

$200-mm$ square plate. Determine the moment of the couple formed by the two

forces $($a$)$ by multiplying their magnitude by their perpendicular distance, $(b)$ by

resolving each force into horizontal and vertical components and adding the

moments of the two resulting couples.

$3\mathrm{.}20$ A piece of plywood in which several holes are being drilled succes$-$

sively has been secured to a workbench by means of two nails. Knowing that the

drill exerts a $5-N*m$ couple on the piece of plywood, determine the magnitude of

the resulting forces applied to the nails if they are located $(a)$ at A and $B,(b)$ at $B$

and $C,(c)$ at A and $C.$

$3\mathrm{.}21$ Four l$-$in$.-$diameter pegs are attached to a board as shown. Two

strings are passed around the pegs and pulled with the forces indicated. $($a$)$ Deter$-$

mine the resultant couple acting on the board. $($b$)$ If only one string is used,

around which pegs should it pass and in what directions should it be pulled to

create the same couple with the minimum tension in the string? $($c$)$ What is the

value of that minimum tension?

$3\mathrm{.}22$ Four pegs of the same diameter are attached to a board as shown.

Two strings are passed around the pegs and pulled with the forces indicated.

Determine the diameter of the pegs, knowing that the resultant couple applied to

the board is $485lb*in.$ counterclockwise.

Do $3\mathrm{.}19-3\mathrm{.}22$