Answer:
5 mg, 
Explanation:
First of all, let's rewrite the mass in grams using scientific notation.
we have:
m = 0.005 g
To rewrite it in scientific notation, we must count by how many digits we have to move the dot on the right - in this case three. So in scientific notation is

If we want to convert into milligrams, we must remind that
1 g = 1000 mg
So we can use the proportion

and we find

Answer:
0.02
Explanation:
coefficient of kinetic friction = μ
force of friction = Ff
Normal Force = FN, but
FN = -W
Ff = -μFN
so μ = Ff/FN
= 4N/200N
= 0.02.
For Newton's second law, the force applied to an object is equal to the product between the mass of the object and its acceleration:

Rewriting the acceleration as the increment of velocity

in a time

:

, F becomes

But given the definition of momentum:

, then

represents the momentum change. So we can rewrite F as

And re-arranging the formula we can calculate the value of the change in momentum: