A 90 N block rests on a horizontal surface. It takes 40 N to get it moving and 25 N to keep it moving. Calculate the coefficients of static and kinetic friction.

The weight of the block is $W = 90 \text{ N}$.
The force required to get the block moving (static friction) is $F_s = 40 \text{ N}$.
The force required to keep the block moving at a constant velocity (kinetic friction) is $F_k = 25 \text{ N}$.

For a block on a horizontal surface, the normal force $F_N$ is equal to its weight $W$.

The formula for static friction is $F_s = \mu_s F_N$.
Rearrange to solve for $\mu_s$:

Substitute the values:

The formula for kinetic friction is $F_k = \mu_k F_N$.
Rearrange to solve for $\mu_k$:

Substitute the values:

The coefficients of friction are:
Static friction coefficient: $\boxed{\text{0.44}}$
Kinetic friction coefficient: $\boxed{\text{0.28}}$