1. ## Friction (check my answer)

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) $u=\frac{f}{N}$
f=28 , N=80
$\frac{28}{80}=0.35$
b)80*28=120*x
$x=\frac{80*28}{120} =18.7N$

Am I correct?

2. first part is correct, second part is incorrect.

Hint: Since N has increased, f has to increase