# NCERT Class 9 Science Solutions: Chapter 10 – Gravitation Part 10

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Question 19:

Q. In what direction does the buoyant force on an object immersed in a liquid act?

An object immersed in a liquid experiences buoyant force in the upward direction.

Question 20:

Q. Why does a block of plastic released under water come up to the surface of water?

Two forces act on an object immersed in water. One is the gravitational force, which pulls the object downwards, and the other is the buoyant force, which pushes the object upwards. If the upward buoyant force is greater than the downward gravitational force, then the object comes up to the surface of the water as soon as it is released within water. Due to this reason, a block of plastic released under water comes up to the surface of the water.

Question 21:

Q. The volume of of a substance is. If the density of water is , will the substance float or sink?

If the density of an object is more than the density of a liquid, then it sinks in the liquid. on the other hand, if the density of an object is less than the density of a liquid, then it floats on the surface of the liquid.

Here,

Density of the substance

The density of the substance is more than the density of water hence; the substance will sink in water.

Question 22:

Q. The volume of a sealed packet is. Will the packet float or sink in water if the density of water is what will be the mass of the water displaced by this packet?