Because a liquid can take the wheight of the hydraulic press while a gas could combust under pressure.
In physical chemistry, the mean free path is the average distance between the atoms during collision. Its formula is

where d is the diameter of the Nitrogen atom (d = 310 x 10^-7 m), Na is Avogadro's number (Na=6.022 x 10^23), R is the gas constant (8.314 J/mol-K), T is the absolute temperature (T= 20 + 273 = 293 K). Substituting the values,
P = 6.32 x 10^-13 Pascals
Answer: 
Explanation:
Given
The frequency of the source is 
Change in frequency is 
Speed of sound 
Suppose
is the velocity of the observer
Doppler frequency is given by

Here, the source is at rest
While approaching source, frequency is

While leaving, frequency is

The difference in the frequency is

If mass doubled and the force remained constant then the acceleration would also double
Hopes this helps
As it is given here that two blocks are pulled towards right side with constant horizontal velocity.
Both blocks are given that moving with speed 2 m/s
Now we can say that by Newton's II law
F = ma
i.e. Net force on a system is product of its mass and acceleration
but as we can see that here two blocks are moving with constant speed so here as per definition of acceleration we will say

As we know that v = constant

so here from 2nd law

so net force must be zero block A
So correct FBD must be "option A"
we should not represent any force on it