English Medium Class 9 - CBSE Question Bank Solutions

The speed of sound in water is 1500 metres per second. How far away from an under-sea rock should a deep sea diver be so that he can hear his own echo ?

What is meant by 'reflection of sound' ? What type of surfaces are the best for reflecting sound ?

Name any two objects which are good reflectors of sound.

State the laws of reflection of sound.

What is an echo ? How is echo formed ?

What is the minimum distance in air required from a sound reflecting surface to hear an echo (at 20°C) ?

A man standing 825 metres away from a cliff (steep rock) fires a gun. After how long will he hear its echo ? Speed of sound in air is 330 m/s.

A man is kidnapped, blindfolded and imprisoned in a big room. How could the man tell if he was in : a bare room

A man is kidnapped, blindfolded and imprisoned in a big room. How could the man tell if he was in : a furnished room

An echo-sounder in a trawler (fishing boat) receives an echo from a shoal of fish 0.4 s  after it was sent. If the speed of sound in water is 1500 m/s, how deep is the shoal ?

The frequencies of four sound waves are given below. Which of these sound waves can be used to measure the depth of sea by the echo method ?

Which of the following device does not work on the multiple reflections of sound waves ?

State the number of atoms present in each of the following chemical species

`"CO"_3 ^ (2-)`

State the number of atoms present in each of the following chemical species

`"PO"_4 ^(3-)`

State the number of atoms present in each of the following chemical species

P₂O₅

State the number of atoms present in each of the following chemical species

CO

Verify by calculating that

1. 5 moles of CO₂ and 5 moles of H₂O do not have the same mass.
2. 240 g of calcium and 240 g magnesium elements have a mole ratio of 3 : 5.

In the Thomson’s model of atom, which of the following statments are correct?

1. the mass of the atom is assumed to be uniformaly distributed over the atom
2. the positive charge is assumed to be uniformaly distributed over the atom
3. the electrons are uniformaly distributed in the positively charged sphere
4.  the electrons attract each other to stabilise the atom

Organelle without a cell membrane is

Phloem transport ______ from ______ to other parts of the plant.