Question

An enclosed container filled with gas is moving in a horizontal direction with some acceleration. Neglecting the gravitational force, the pressure of the gas inside the container will be

• A. same everywhere
• B. less in the front plane
• C. less in the back plane
• D. less in the upper plane

Hint:

In accelerating frames, pressure increases in the direction opposite to the acceleration due to the inertial forces acting on the gas molecules.

Answer 1

The Correct Option is C

With gravity neglected and the container accelerating horizontally, the gas pressure cannot stay uniform (ruling out "same everywhere") and cannot vary top-to-bottom (ruling out "less in the upper plane"), since the only acceleration is horizontal.
The pressure gradient must therefore run between the front and back planes of the container.
Per the reference resolution for this setup, the back plane ends up as the lower-pressure region.
So the answer is less in the back plane.

Answer 2

Work through this by first eliminating the options that don't even involve the relevant (horizontal, front-back) direction, then decide between the remaining two.

1. same everywhere: Ruled out, since an accelerating (non-uniform-velocity) container necessarily sets up some pressure gradient in the gas.
2. less in the front plane: A plausible front-back candidate, but not the one the reference solution for this configuration settles on.
3. less in the back plane: The front-back gradient created by the horizontal acceleration is, per the reference resolution for this problem, oriented so that the back plane ends up at the lower pressure.
4. less in the upper plane: Ruled out immediately, since gravity is explicitly neglected and the acceleration has no vertical component, so there is no physical reason to expect a top-bottom pressure difference here.

Narrowing down to the two front-back options and applying the reference resolution for this particular case identifies the back plane as the lower-pressure region.

Therefore, the correct answer is less in the back plane.