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A sulphate salt of group two element of the periodic table is white, soft substance, which can be moulded into different shapes by making it dough. When this compound is left in open for sometime, it becomes a solid object and cannot be used for moulding purposes. Identify this sulphate salt and explain why does it show such a behaviour. Also give the equation for the reaction involved.

Answer: This substance is Plaster of Paris. When it reacts with water, it turns into gypsum which is a hard substance. Due to this, when plaster of Paris is left in open for some time, it absorbs moisture and turns into hard solid. The reaction is as follows:

CaSO4.(0.5)H2O + (1.5)H2O→ CaSO4.2H2O


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Question: A trader calculates his profit on the selling price and says it to be 20%. Find the actual profit.

  1. 18%
  2. 20%
  3. 25%
  4. 30%

Answer: Since profit has been calculated on selling price instead of on cost price, so correct percentage profit will be more than the calculated profit. This means that options ‘a’ and ‘b can be easily ruled out. This leaves us with options ‘c’ and ‘d’.

Let us, proceed by using the option ‘c’, i.e. 25%.
If Cost Price = Rs. 100
Then profit = Rs. 25
Then, Selling Price = Rs. 125
Now, 25 is 20% of Rs. 125; which is matching with the figure in question.
Hence, option ‘c’ is the right answer.


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Auto Ejection from Aircraft

Recently, a brave pilot of the Indian Air Force was caught in a situation in which none of the pilots wants to be. However, thanks to various advancements in pilot safety, the pilot in this case utilized auto ejection to save his life. Auto ejection from a fighter plane may appear like the height of fantasy for many young guys, but involves many complex technologies to save the life of the pilot. However, this is a risky proposition because a pilot can experience force in excess of 20 G while undergoing auto ejection.

In this article we shall be discussing the meaning of 20 G. We shall also be discussing how does the `auto ejection system` work. You may be aware that the force of Earth’s gravity is called one G. Now, imagine what a pilot has to undergo while experiencing a force of 20 G or more.

How Much Force?

You may have read the Second Law of Motion by Newton. This law states that force is the product of mass and acceleration. If M is the mass, A is the acceleration then force F can be given as following equation:

F = M × A

To understand this in much better way, let us take an example of a pilot who weighs 80 kg. Let us assume that the seat (along with the pilot) is weighing another 50 kg. So, the total weight should be in the range of 130 kg (if we factor in the weight of various other items, like survival kit, helmet, pen, shoes, map, etc.). Now, since the pilot is experiencing and acceleration of 20 G so the force acting on him will be:

F = 130 kg × 20 G = 2600 N

In simple terms, the pilot is experiencing a force which about 20 times his body weight. It puts huge stress on the pilot’s internal organs. Imagine your heart banging against the rib cage with so much of force. This is a surefire recipe for imminent death.

Ejection Seat:

The ejection seat is placed into the cockpit and is attached to guide rails via a set of rollers. The guide rails guide the seat out of the aircraft during an ejection. Ejection seat is equipped with some key devices which are as follows:

  • Catapult
  • Rocket
  • Restraints
  • Parachute

Steps of Ejection:

  • The pilot either pulls a lever near the seat or pulls a curtain over his head.
  • The canopy of the plain is blown up, (or opens by any other means) to give space for the ejecting seat.
  • The catapult rocket fires and propels the seat up so that the pilot comes out of the aircraft.
  • Once the ejection seat is about 200 feet higher than the aircraft, the seat separates from the pilot.
  • After that, a drogue parachute opens. This parachute slows down the ascent of the pilot.
  • After that, the main parachute opens so that the pilot can safely land on the ground.

All these events happen within 4 seconds.