RRB JE Mechanical flashcards

31 cards. Read the term and the definition here. The deck at the top of this page is optional.

HCF-LCM relation

For any two positive integers a and b, HCF(a, b) × LCM(a, b) = a × b. This relation applies to two numbers only; for three or more numbers it does not hold directly.

Successive percentage change

A net change after an a% change followed by a b% change equals a + b + ab/100 percent. Thus a 20% increase then a 10% decrease gives a net 8% increase.

Compound interest formula

CI = P[(1 + r/100)^n − 1], where P is principal, r is the annual rate in percent and n is the number of years. For half-yearly compounding, use r/2 and 2n.

Average speed equal distances

If a body covers two equal distances at speeds x and y, its average speed is 2xy/(x + y), the harmonic mean. It is not the arithmetic mean (x + y)/2.

Quadratic roots

For ax² + bx + c = 0, the sum of roots is −b/a and the product is c/a. The discriminant b² − 4ac decides whether roots are real, equal or complex.

Letter position mnemonic EJOTY

E = 5, J = 10, O = 15, T = 20 and Y = 25. These anchors let you find nearby alphabet positions quickly in coding-decoding and series questions.

Syllogism some conversion

The statement Some A are B always implies Some B are A. However, All A are B does not imply All B are A unless the reverse statement is also given.

Clock hand angle formula

The angle between the hour and minute hands is |30H − 5.5M| degrees, where H is the hour and M is the minutes. If it exceeds 180°, subtract it from 360°.

Blood relation tree convention

In family-tree diagrams, vertical lines show parent-child generations and horizontal lines show siblings or spouse. People in the same generation appear on the same level.

Article 51A

Article 51A lists the Fundamental Duties of Indian citizens. It was added by the 42nd Amendment in 1976 on the recommendation of the Swaran Singh Committee.

RBI establishment

The Reserve Bank of India was established on 1 April 1935 under the RBI Act 1934, was nationalised in 1949 and has had its central office in Mumbai since 1937.

Indian Standard Time

IST is based on longitude 82.5°E and equals UTC + 5:30. India uses one time zone although the sun rises about two hours earlier in the northeast.

Mitochondria function

Mitochondria are called the powerhouse of the cell because they carry out aerobic respiration and produce ATP, the energy currency used for most cellular work.

Blood pH and pressure

Normal arterial blood pH is about 7.35–7.45, slightly alkaline. Normal adult blood pressure is about 120/80 mmHg, where 120 is systolic and 80 is diastolic pressure.

Ohm's law

At constant temperature, the current through a conductor is directly proportional to the potential difference across it: V = IR, with V in volts, I in amperes and R in ohms.

Universal blood donor

O negative red blood cells can be given to recipients of any ABO and Rh type in emergencies. AB positive is the universal red-cell recipient.

First law of thermodynamics

For a closed system, ΔQ = ΔU + W, where ΔQ is heat supplied, ΔU is change in internal energy and W is work done by the system.

Ideal gas equation

PV = nRT relates pressure, volume, moles and absolute temperature, with R = 8.314 J mol⁻¹ K⁻¹. One mole occupies 22.4 litres at STP.

Le Chatelier's principle

When a system at equilibrium is disturbed by a change in concentration, pressure or temperature, the equilibrium shifts in the direction that opposes the disturbance.

pH definition

pH = −log₁₀[H⁺]. At 25°C, pH below 7 is acidic, 7 is neutral and above 7 is basic. Each unit means a tenfold change in hydrogen-ion concentration.

Mole concept

One mole contains 6.022 × 10²³ particles, the Avogadro number. Molar mass in grams equals one mole, and molarity is moles of solute per litre of solution.

RAM versus ROM

RAM is volatile working memory that loses its contents when power is off and is read/write. ROM is non-volatile memory that retains data and is mainly read-only.

IPv4 address size

An IPv4 address is 32 bits long, written as four dotted decimal octets such as 192.168.0.1. IPv6 uses 128 bits to overcome IPv4 address exhaustion.

Undo and redo shortcuts

Ctrl+Z undoes the last action in most Windows applications. Ctrl+Y redoes or repeats the undone action. Ctrl+S saves the file and Ctrl+P opens print.

Absolute cell reference

In a spreadsheet, $A$1 is an absolute reference that stays fixed when a formula is copied. A1 is a relative reference that adjusts to the new cell location.

BOD as pollution indicator

Biochemical Oxygen Demand measures the oxygen consumed by microbes to decompose organic matter in water over five days. Higher BOD indicates greater organic pollution.

Montreal Protocol

The 1987 Montreal Protocol controls the production and consumption of ozone-depleting substances such as CFCs and halons in order to protect the stratospheric ozone layer.

Environment Protection Act 1986

India's umbrella environmental law was enacted after the Bhopal gas tragedy. It empowers the central government to set emission standards and provides the framework for EIA notifications.

Otto cycle efficiency

Air-standard Otto efficiency is 1 − 1/r^(γ−1), where r is the compression ratio and γ is the specific heat ratio. Higher r or lower γ raises efficiency.

Reynolds number

Re = ρVD/μ is the ratio of inertial to viscous forces. In pipe flow, Re below about 2000 is laminar, 2000–4000 transitional and above 4000 turbulent.

Bernoulli equation

For steady, incompressible, frictionless flow along a streamline, P/ρg + V²/2g + z is constant. The equation expresses conservation of energy per unit weight.