Upthrust In Fluids, Archimedes

Question 1

Upthrust or buoyant force

Answer 1

When a body is partially or wholly immersed in a liquid, an upward force acts on it called as such

Question 2

Buoyancy

Answer 2

Property of liquid to exert an upward force on a body immersed in it

Question 3

Buoyancy can be demonstrated using which 2 experiments?

Answer 3

Pushing an empty can into water and pushing a cork into water

Question 4

When a can is put in a tub of water, two forces act on it. Which ones?

Answer 4

Its weight and upthrust due to water

Question 5

Why is an external downward force needed to keep a can immersed in water?

Answer 5

To balance the net upward force (by upthrust)

Question 6

True or false: gases have the property of buoyancy.

Answer 6

True

Question 7

Why do we not feel a buoyant force due to air?

Answer 7

It is negligibly small as compared to our own weight

Question 8

Why does a balloon filled with hydrogen rise up?

Answer 8

The upthrust or buoyant force on balloon due to surrounding air is more than the weight of the balloon filled with the gas that is less denser than air

Question 9

What does the upthrust depend on?

Answer 9

Submerged portion of body and density of fluid

Question 10

If force due to buoyancy is greater than the weight of the body, what will happen to the body when it is placed in the liquid?

Answer 10

Float with body partially immersive inside liquid

Question 11

If the force due to buoyancy is equal to the weight of the body, what will happen to the body when it is placed in the liquid? 

Answer 11

Float with the whole of it just immersed inside the liquid

Question 12

Apparent weight of a floating body

Answer 12

0

Question 13

If force due to buoyancy is less than the weight of the body, what will happen to the body when it is placed in the liquid? 

Answer 13

It will sink

Question 14

Mathematically represent the acceleration with which a body will sink in a liquid.

Answer 14

It will sink down into the liquid with an acceleration a such that ma = W - Fb or a = (W - Fb)/m (ignoring the viscous force of the liquid)

Question 15

Unit of upthrust

Answer 15

N or kgf

Question 16

Larger the volume of a body is submerged in a fluid, effect on upthrust?

Answer 16

Greater upthrust

Question 17

For the same volume of a body inside a fluid, more the density of fluid, effect on upthrust?

Answer 17

Greater upthrust

Question 18

Upthrust acts on a body in which direction and where?

Answer 18

In the upward direction and at the centre of buoyancy

Question 19

Where is the centre of buoyancy?

Answer 19

Centre of gravity of displaced fluid

Question 20

When a bunch of feathers and a pebble of same mass are allowed to fall in air, the pebble falls faster than the bunch of feathers. Why?

Answer 20

Upthrust due to air on pebble is less than that on the bunch of feathers because the volume of pebble is less than that of the bunch of feathers of same mass

Question 21

If we want to immerse a cork in glycerine to the same extent as a cork in water, then additional force is needed on the first cork to immerse it to the same level as the second cork. Why?

Answer 21

Since density of glycerin is more than that of water and (for the same volume of body) denser liquid exerts a greater upthrust, more force is required to counteract the greater upthrust in glycerin (if we want to bring cork to same level as in water).

Question 22

A liquid contained in a vessel exerts pressure…

Answer 22

At all points and in all directions

Question 23

The pressure at a point in a liquid is _____ in all directions (Upwards, downwards, and sideways)

Answer 23

Same (even upwards?)

Question 24

True or false: Pressure decreases with depth inside the liquid.

Answer 24

False

Question 25

Why does upthrust occur?

Answer 25

When a body is immersed inside a liquid, the pressure exerted upwards on the lower face of the block which is at a greater depth is more than the pressure exerted downwards on the upper face of the block which is at a lesser depth. Thus, there is a difference in pressure which leads to a net upward force known as upthrust.

Question 26

Why is there no thrust on the side walls of the body?

Answer 26

The thrust the body experiences on both sides are equal in magnitude and opposite in directions— so they get neutralised 

Question 27

Why does a lamina sink in a liquid?

Answer 27

A lamina is so thin that the pressure on both its surfaces will be nearly the same in the liquid, causing the liquid to exert negligible upthrust and it to sink into the liquid due to its own weight.

Question 28

When a body is immersed in a liquid, of the rest on it due to liquid is equal to what?

Answer 28

Weight of the liquid displaced by the submerged part of the body

Question 29

What is the effect of upthrust on the weight of a body immersed in liquid?

Answer 29

The weight of the body appears to be less than its actual weight

Question 30

What does Archimedes principle state?

Answer 30

When a body is immersed partially or completely in a liquid, it experiences an upthrust, which is equal to the weight of the liquid displaced by it.

Question 31

What is the average density of a hollow body?

Answer 31

The ratio of mass of the body (=Mass of material of body + mass of air enclosed) to its total volume

Question 32

What is density?

Answer 32

Mass per unit volume

Question 33

True or false: density is a vector quantity.

Answer 33

False

Question 34

How can we represent density using symbols?

Answer 34

d or p (rho)