**Answer: Option D**

# Category Archives: 06 Pressure

## Watch “Michelin and General Motors Unveil Airless, Puncture-proof Tires” on YouTube

## Marshmallow Hulk in Vacuum Jar

When the pump is switched on and the air in the jar is gradually removed, the pressure in the jar decreases. There will be fewer air molecules per unit volume in the far. Hence rate of collision of the air molecules with one another and with the wall and hulk will be reduced. As pressure P = F/A, the force acting per unit area decreases, the pressure decreases.

In the marshmallow, there are pockets of air at normal atmospheric pressure initially. As the pressure in the jar decreases, the pockets of air in the marshmallow expands due to this pressure difference. Hence the hulk expands and its volume increases.

## Liquid Pressure Summary Part 2

## Another P1V1 = P2V2 question

Solution: Option C

## When to use the concept PV = constant and P1V1 = P2V2 to solve?

When **temperature is constant** (for o-level), when a __fixed mass of gas (fixed number of air molecules)__ is __compressed__ in a closed system (e.g. piston), the __volume V decreases__ and __pressure P increases__, and vice versa.

But when you multiply pressure and volume, PV, it is always a constant.

**PV = constant**

Hence we can always equate the PV of the first scenario = to the PV of the second scenario, provided there is no addition or removal of air molecules from the system.

Hence, you have **P1V1 = P2V2**

The followings are 4 different questions which require this concept to solve. Do revise them.

**Solutions: Option D** (refer to the worked solutions below)

**Solutions: Option D**

**Solutions: A**

4)

**Solutions:**

5)

**Solution: Option C**