Answer:
I got:
u
s
=
0.51
F
=
78.4
N
Explanation:
At the start the
100
N
force is just enough to overcome static friction so we can write:
Force
=
Static Friction
F
=
μ
s
N
where
μ
s
is the coefficient of static friction and
N
=
Normal Reaction that in an horizontal case such this will be equal to the weight of the block, so
N
=
m
g
.
We get:
F
=
μ
s
⋅
m
g
in numbers:
100
=
μ
s
⋅
20
⋅
9.8
μ
s
=
100
20
⋅
9.8
=
0.51
