Question Discussion & Solution

Total number of people = 45

Position of A from the behind = 26^th

Position of A from the front = Total number of people – A’s position from the behind + 1

= 45 – 26 + 1

= 20^th

CONCEPT:

• Supersonic speed: An object moving with a speed greater than the speed of sound is said to move with a supersonic speed.
  • Generally, a bullet fired from a gun and aircraft moves with supersonic speed. 
  • The speed of sound is about 768 miles per hour (1,236 kilometers per hour) at sea level.
• Supersonic speeds are described by their "Mach number".
• Mach number: The ratio of the speed of the object to the speed of sound in the air of the same temperature and density is called Mach number.
  • Supersonic includes speeds up to five times faster than the speed of sound, or Mach 5.

EXPLANATION:

• When the speed of any object exceeds the speed of sound, it is said to be traveling at Supersonic speed. So option 2 is correct.

EXTRA POINTS:

• Subsonic has a speed of less than 0.8 Mach.
• Hypersonic may have a speed between 5-10 Mach.

The correct option is 2 i.e. Sodium Carbonate

Key Points

• Sodium Carbonate is also known as washing soda it is a salt of carbonic acid.
• Sodium carbonate can be manufactured by Solvay's process.
• It is used for treating hard water and industrial detergent mixtures.
• The aqueous solution of sodium carbonate is alkaline.
• Calcium Sulphate exists in the forms of white solids and is not soluble in water.
• Plaster of Paris and Gypsum are its hydrates.

An electrician wears rubber gloves to avoid electric shock while repairing an electrical switch.

• As the human body is a good conductor of electricity.
• So it can pass through electricity from itself when it comes in contact with electricity and may get shocked or even fatality.
• As rubber is an insulator i.e. it is a non-conductor of electricity.
• So it protects the body of electricians from direct contact with electricity.

Rupee, Pound and Yen are types of currency.