(English Medium) ICSE Class 9 - CISCE Question Bank Solutions

The S.I. unit of upthrust is : 

A body weighs 450 gf in air and 310 gf when completely immersed in water. Find 

(i) The volume of the body,

(ii) The loss in weight of the body, and

(iii) The upthrust on the body.

State the assumption made in part (i). 

You are provided with a hollow iron ball A of volume 15 cm³ and mass 12 g and a solid iron ball B of mass 12 g. Both are placed on the surface of water contained in a large tub.

1. Find upthrust on each ball.
2. Which ball will sink? Give a reason for your answer (Density of iron = 8.0 g cm^-3) 

Two spheres A and B, each of volume 100 cm³ is placed on water (density = 1.0 g cm⁻³). The sphere A is made of wood of density 0.3 g cm⁻³ and sphere B is made of iron of density 8.9 g cm⁻³.

1. Find:
   1. The weight of each sphere, and
   2. The upthrust on each sphere.
2. Which sphere will float? Give reason.

The mass of a block made of certain material is 13.5 kg and its volume is 15 × 10^-3 m³.

(a) Calculate upthrust on the block if it is held fully immersed in water.

(b) Will the block float or sink in water when released? Give a reason for your answer.

(c) What will be the upthrust on block while floating?

Take density of water = 1000 kg m^-3. 

A block of wood is floating on water with its dimensions 50 cm x 50 cm x 50 cm inside water. Calculate the buoyant force acting on the block. Take g = 9.8 N kg^-1. 

A body of mass 3.5 kg displaces 1000 cm³ of water when fully immersed inside it. Calculate:

1. the volume of body,
2. the upthrust on body and
3. the apparent weight of body in water. 

Complete the following sentence.

Mass = .................... × density

A homogeneous block floats on water (a) partly immersed (b) completely immersed. In each case state the position of centre of buoyancy B with respect to the centre of gravity G of the block.

Figure shows the same block of wood floating in three different liquids A, B and C of densities ρ₁, ρ₂  and ρ₃ respectively. Which of the liquid has the highest density? Give a reason for your answer.

What is the centre of buoyancy? State its position for a floating body with respect to the centre of gravity of the body. 

A balloon filled with helium gas floats in a big closed jar which is connected to an evacuating pump. What will be your observation, if air from the jar is pumped out? Explain your answer. 

Two identical pieces, one of ice (density = 900kg per meter cube) and other wood (density = 300kg per meter cube) float on water.

1. Which of the two will have more volume submerged inside water
2. Which of two will experience more upthrust due to water.

A body is held inside water contained in a vessel by tying it with a thread to the base of the vessel. Name the three forces that keep the body in equilibrium, and state the direction in which each force acts. 

What do you mean by reflection of light? 

State which surface of a plane mirror reflects most of the light incident on it: the front smooth surface or the back silvered surface. 

Explain the following term:

Reflected ray. Draw diagram/diagrams to show them. 

Explain the following term:

Angle of incidence. Draw diagram/diagrams to show them. 

Explain the following term:

Angle of reflection. Draw diagram/diagrams to show them.

With the help of diagrams, explain the difference between the regular and irregular reflection.