w
e
i
g
h
t
o
f
b
l
o
c
k
i
n
n
e
w
t
o
n
s
W
4
0
c
o
e
f
f
i
c
i
e
n
t
o
f
s
t
a
t
i
c
f
r
i
c
t
i
o
n
µ
s
0
.
2
t
o
s
t
a
r
t
m
o
v
i
n
g
:
F
=
f
s
=
µ
s
F
N
F
N
=
W
F
=
µ
s
W
F
=
0
.
2
×
4
0
F
=
8
.