Solution of physics online class test 3 of class 8

 1.A cylinder whose cross -sectional area is 200cm² and height is 20 dm, has a mass of 20 kg.The maximum capacity of cylinder is

Ans.A=200cm²

           = 200/10000 m²

           =2/100 m²

h= 20 dm

 =20×10-¹ m

= 20/10 m

 = 2 m

V= A× h

= 2/100 m² × 2 m

= 4/100 m³

= 0.04 m³

= 4×10⁴ cm³

=40× 10³ cm³

= 40 litre.

 = 40× 1 litre

 40 dm³ ( 1litre = 1 dm³) 

=40 × 10³ cm³

 = 4× 10⁴cm³

=4×10⁴× 1cm³ 

= 4× 10⁴× 10-⁶ m³  (1cm= 10-⁶ m³)

=4× 10-² m³

So, the correct option would be all of these.

2.A cylinder of radius 70 cm and a height of 100 cm has a maximum volume of

Ans.r= 70cm

h= 100cm

V=?

V= πr²h

V= 22/7 × 70cm × 70cm × 100cm.  (π=22/7)

= 22×10cm×7000cm²

=1540 × 10³ cm³

= 1540 L.        ( 1L=1000 cm³)

3.Density of an aluminium is 2.7 g cm-³.54 g of an aluminium block is put in a measuring cylinder with its reading as 27 mL.The level of liquid in cylinder raises to

Ans.M=54g

ρ=2.7 g cm-³

V₁ = 27 mL

V₂ = ?

ρ= M/V

ρ× V = M

 V= M/ ρ

= 54g / 2.7 g cm-³

= 20 cm³

V₂= V₁ + V

    = 27 mL + 20 mL

= 47 mL

4.Density of water is maximum at 4 °C and volume at that temperature would be

Ans. Minimum.

5.A specific gravity bottle is used to measure

Ans. Density.

6.The volume of water is maximum at

Ans. Hundred degree Celsius.

7.Density of a body can not be 

Ans.  negative.

8.On heating water beyond 10° C

Ans. Density decreases due to increase in volume because of thermal expansion.

9.A cuboidal piece of stone 25 cm long,12 cm wide and 8 cm thick has 4 kg mass

Ans.l=25 cm

b= 12cm

h= 8cm

V=?

V= l×b×h

    = 25/100 cm × 12/100 cm × 8/100 cm

    = 0.25 ×0.12×0.8 m³

   =0.024 m³

M= 4 kg

ρ= M/ V

  = 4 kg / 0.024 m³

  = 166.666 kgm-³

  = 166.67 kgm-³.

   Density in gcm-³ come out as 0.16667 gcm-³

So, the correct option is none of these.

10.A 2m heigh piece of ice is seen floating in a river .uniform cross-sectional area of ice is 4000 dm².The volume of ice would be

Ans.h=2 m

A= 4000 dm²

   =4000 × 1 / 100 m²

   =40 m²

V= l×b×h

    = A× h

 V= 40 m² × 2 m

    = 80 m³

This is the volume of ice which is above the water.

We know that 1/10th part of a ice is above the water.

so total volume of ice would be ten times of the volume of ice above the water surface.

V = 80 m³ ×10

     = 800 m³

11.The mass of density bottle is 51.50 g when empty,76.50 g when full of water and 71.85 g when full of oil,then

Ans.M₁=51.50 g

M₂=76.50 g

M₃= 71.86 g

V of water = M₂- M₁

                    = 76.50 g - 51.50g

                    = 25.0 g

since density of water is 1 gram per centimetre cube. 25 gram of water would occupy a volume of 25 cm cube.

V= 25 cm³

ρ= M/ V

   = 71.86 g - 51.50 g / 25 cm³

  = 20.36 g / 25 cm³

  = 0.814 gcm-³

V= 25 cm³ &  ρ=0.814 gcm-³ both are correct.

So right option is C) both a and b.

12.The mass of an empty density bottle is 29.5 g .when filled completely with water is 49.5 g and when completely filled with liquid it is 48.3 g

Ans.M₁= 29.5 g

M₂=49.5 g

 M₃= 48.3 g

ρ=?

ρ relative density= M₃ -M₁ /  M₂ - M₁

   = 48.3g - 29.5 g / 49.5 g - 29.5 g

  = 18.8g / 20g

  = 0.94

But relative density= density of a substance /density of water at 4 degree Celsius.

RD=ρₛ / ρ of water

RD × density of water= density of substance

0.94 × 1gcm-³ =density of

0.94× 1000 kgm-³ =density of a substance

940 kgm-3= density of substance.

13.Calculate volume of wood of mass 12000 kg if the density of wood is 0.8 g cm-³

Ans.m=1200kg

ρ= 0.8 gcm-³

V=?

ρ= M/ V

ρ× V = M

⇒V= M/ρ

      = 12000 kg / 800kgm-³

      = 120/8 m³

      = 15 m³.