# Solution of the Buoyant Force Test

## Physics lesson, the buoyancy force subject. The floating, sinking and suspended objects in liquids. The buoyant force applied to the objects in liquid. Solutions of the buoyancy force test.

Solution – 1

The formula for floating objects on liquid.

Vs
 = ρo ρl
V

1
 = ρ0 1.2
4

ρo = 0.3 g/cm3

The right answer is A option.

Solution – 2

We will find the density of the liquid, using the density of the K body. Then, we will find the density of the L body, using the density of the liquid.

Density of the liquid X.

Vs
 = ρk ρx
V

1
 = 0.8 ρx
4

ρx = 3.2 g/cm3

Density of the L object,

Vs
 = ρL ρx
V

2
 = ρL 3.2
3

ρL = 2.13 g/cm3

The right answer is E option.

Solution – 3

The K object is sinking in different amounts in the different liquids.

Using the rate of sinking K object, we can find the density of the Y liquid .

Firstly, we must find density of the K object.

In figure -1

2
 = ρK 800
4

ρK = 400 kg/m3

Now, using the density of the K object, we can find the density of the Y liquid.

1
 = 400 ρY
4

ρY = 1600 kg/m3

The right answer is C option.

Solution – 4

Let we find density of the K body.

1
 = ρK 1.5
3

ρK = 0.5 g/cm3

Let we find weight of the K body.

W = ρ • V • g

WK = 0.5 • 600 •10

WK = 3000 g

WK = 3 kg

The magnitude of the buoyancy force applied to the K body is equal to the sum of the weight of the K and L bodies.

The buoyancy force is found as following.

F = Vs• ρl • g

F = 600 • 1.5 • 10

F = 9000 g

The buoyancy force applied to the K and L objects is 9000 g. We found the weight of the K object at above as 3000 g.

The weight of the L object.

WL = 9000 – 3000

WL = 6000 g

Let we find the density of the L object. The volume of the L object is 400 cm3.

W = V • ρ• g

6000 = 400 • ρL • 10

 ρL = 6 4

ρL = 1.5 g/cm3

The right answer is B option.

Solution – 5

The expression in the D option is wrong.

The buoyant force applied to floating objects on the liquid can not found by multiplying of volume of the object and density of the liquid.

The buoyant force is found by multiplying the volume of sinking portion of the object with density of the liquid and gravity acceleration, in every situation.

F = Vs • ρ• g

The right answer is D option.

Solution – 6

We must find the buoyant force that the X liquid applies to the K object for to find the dynamometer indicate value in the X liquid.

To calculate the buoyant force, we must know the volume of the K object.

The volume of the K object can be found using buoyant force of the X liquid.

If the weight of the K object is 40 N in the X liquid.

F = 100 – 40

F = 60 N

The buoyant force that the X liquid applies to the K object is 60 N.

60 = Vs • 1200 • 10

Vs = 0.005 m3

Let we find density f the K object.

100 = 0.005 • ρK • 10

ρK = 2000 kg/m3

If this object is put in the Y liquid, the buoyant force that the Y liquid applies to the K object will be equal to the weight of the K object. The object will be stayed hanging in the Y liquid.

Therefore, the dynamometer indicates 0 value.

The right option is A

Buoyant Force Questions

Buoyant Force In Liquids

RISE KNOWLEDGE

24/08/2018

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