$(16-18)$ A $3$ kg block remains at rest on a horizontal surface. Use g $=10$ m$/$s$2.$

$16.$ The net force acting on the block is $\_\_\_\_\_\_\_\_$ N$.$

a$)40$

b$)30$

c$)20$

d$)10$

e$)$ none of the above is correct

$17.$ The friction force on the block is $\_\_\_\_\_\_\_\_$ N$.$

a$)40$

b$)30$

c$)20$

d$)10$

e$)$ none of the above is correct

$18.$ Which force listed below does not have a $3$rd Law pair$($reaction force$)?$

a$)$ Earth pulls down on the block

b$)$ The surface pushes up on the block

c$)$ The block pulls up on the Earth

d$)$ The block pushes down on the surface

e$)$ misleading question $$ all forces are part of a $3$rd Law pair

$(19-21)$ A string is attached to the block $($from problem above$)$ and the block is now pulled to the right

with a horizontal tension force of $6$ N$.$ While this force is applied, the block slides with a constant

speed of $2$ m$/$s $.$ Use g $=10$ m$/$s$2.$

$19.$ The kinetic friction force on the block is $\_\_\_\_\_\_\_\_$ N$.$

a$)12$

b$)10$

c$)8$

d$)6$

e$)$ none of the above is correct

$20.$ The coefficient of kinetic friction is $\_\_\_\_\_\_\_\_.$

a$)0\mathrm{.}1$

b$)0\mathrm{.}2$

c$)0\mathrm{.}3$

d$)0\mathrm{.}4$

e$)0\mathrm{.}5$