The acceleration f required to accelerate a rectangular tank containing water horizontally so that the slope of its free surface is 45°, is

Let mass be
m
and area of cross section be
A

Consider
F
i
g
.
1
, Equilibrium condition
(
P
2
−
P
1
)
A
=
m
g
=>
P
2
>
P
1
−
−
−
−
−
(
1
)

Consider
F
i
g
.2
, Applying Newton law considering acceleration ‘
a
‘ rightward
(
P
2
−
P
1
)
A
=
m
a
=>
P
2
>
P
1
−
−
−
−
−
(
2
)