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.
Steel is a hard magnetic material. When magnetized, it is not as strong as soft iron. But steel retains its magnetism, hence it is used to make permanent magnets e.g compass need, speaker, fridge door.
Iron is a soft magnetic material. It can be easily and strongly magnetised. But it loses its magnetism easily. Hence it is used to make temporary magnet e.g. Electromagnet.
Do remember that compass is like a freely suspended magnet. It is made of steel!
There are 3 scenarios with slight variations.
Calculate the force F needed to pull the block up the inclined plane.
View the video below to understand how to solve these types of question.
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