$19-21)$ 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$)0\mathrm{.}4$

$15.$ How much work did kinetic friction from the surface below do on the $4$ kg block during this process?

a$)-2$ J

b$)-6$ J

c$)-10$ J

d$)-14$ J

e$)-18$ J

$16.$ How much work did static friction from the $1$ kg block above do on the $4$ kg block during this process?

a$)+2$ J

b$)+6$ J

c$)+10$ J

d$)+14$ J

e$)+18$ J

$17.$ What is the coefficient of kinetic friction between the $4$ kg block and the surface below?

a$)0\mathrm{.}35$

b$)0\mathrm{.}30$

c$)0\mathrm{.}25$

d$)0\mathrm{.}20$

e$)0\mathrm{.}1$