A source of sound A emit waves of frequency 1800 Hz is falling towards ground with a terminal speed v. The observer B on the ground directly beneath the source receives waves of frequency 2150 Hz. The source A receive waves, reflected from ground, of frequency nearly: (Speed of sound =343 m⋅s−1) A. 2150 Hz B. 2500 Hz C. 1800 Hz D. 2400 Hz

I want  complete notes on the chapter friction 

In my book subtopics are:

Friction 

Types of friction 

Factors affecting friction 

Methods of reducing friction 

Methods of increasing friction 

Advantages and disadvantages of friction 

Some real life based situation where friction is applied.

How to make a monomer into polymer if it is an addition polymer example

This planet, _______ is yellowish in colour and has many rings and satellites.

A. Uranus

B. Jupiter

C. Neptune

D. Saturn

Pasteurized milk does not need to be boiled. Why?

Write the $pH$ value of the

1. Saliva (before meal)

2. Saliva (after meal)

3. Lemon juice

4. Colourless aerated drink

5. Carrot juice

6. Coffee

7. Tomato juice

8. Tap water