An 80N wooden block is placed on top of a wooden table.If a force of 28N is necessary to keep the block moving at a constant velocity.

a)What is the co-efficient of sliding friction for the wooded block?

b)if a wieght of 40N is placed on top of the wooden block what force will be required at a constant velocity across the table?

Attempt:

a)$\displaystyle u=\frac{f}{N} $

f=28 , N=80

$\displaystyle \frac{28}{80}=0.35 $

b)80*28=120*x

$\displaystyle x=\frac{80*28}{120} =18.7N $

Am I correct?