Mechanical Knowledge

Q2.For the same compression ratio the thermodynamic cycles in the order of decreasing efficiencies are (A) Dual, Diesel, Otto (B) Dual, Otto, Diesel (C) Diesel, Dual, Otto (D) Otto, Dual, Diesel Ans: (C) Diesel, Dual, Otto *for same compression ratio Otto cycle work on high efficiency as compare to diesel cycle.. because diesel cycle work on compressed air fuel mixture ignition that don't have spark plug due to this clearance volume of diesel cycle is less and compression ratio is high as compare to Otto cycle. *compression ratio:      =Total volume of cylinder/clearance volume of cylinder  =V/Vc Compression ratio look like 14:1 that means  Total volume of cylinder =14 Clearance volume of cylinder =1

 Q1  A 10kg solid at 100°C with a specific heat of 0.8 kj/kg°C is immersed in 40 kg of 20°C liquid with a specific heat of 4.0 kj/kg°C estimate the temperature after a long time if the Container is insulated (specific heat of water = 4.18 kj/kg). (A) 30°C (B) 28°C (C) 26°C (D) 24°C Ans: (D) 24°C Solution: *Q=mc ΔT Q=Heat addition  m=mass c= specific heat  ΔT= change in temperature  Heat given by solid = Heat taken by water 10×0.8×(100-T)= 40×4×(T- 20) 800 - 8T = 160T - 3200       4000 = 168T T = 23.8°C = 24°C

 Q1. Wet clothes are hanged on a clothesline outdoors in sub-zero weather. After a day, the clothes are brought into the house and observed to be dry. The process of drying is best explained as (A) vaporization (B) sublimation  (C) melting  (D) condensation  Ans: (B) sublimation  *sub-zero weather=  temperature of environment below 0° Centigrade in india and in United States below 0° Fahrenheit  *Sublimation : phase transition of substance from solid to gas state, without passing through the liquid state Solid  ------sublimation------------> Gas     Solid <----------------Desublimation---Gas Solid --------- melting---------------->liquid Solid <----------- freezing------------liquid Liquid ------------- vaporization------> Gas  Liquid<--------------- condensation----- Gas Question 2. Your finger sticks to an ice tray just taken from the refrigerator.  Which factor has more effect on this phenomenon? (A) the inside temperature of the freezer  (B) the humidity of the ai

 Q1. What is Anodising  (A) a process of coating of zinc by hot dipping  (B) a zinc diffusion process (C) a process used for making thin phosphate coating on steel to act as a base or primer for enamels and paints (D) an oxidizing process used for aluminum and magnesium articles Ans (D) an oxidizing process used for aluminum and magnesium articles  *Anodising:- Anodising is an electrolytic process for producing thick oxide layer(coating), usually on aluminium and its alloys. The oxide layer is typically 5 to 30 micro meter in thickness and is used to give improved surface resistance to wear and corrosion,  or as a decorative layer.

 Q1.Following gases are used in tungsten inert gas welding (A) CO2 and H2 (B) Argon and neon (C) Argon and helium (D) Helium and neon Ans (C) Argon and helium  Q2. The function of a washer is (a) To fill the axial gap (b) To provide cushioning effect (c) To absorb shocks and vibrations (d) To provide bearing area Ans: (d) To provide bearing area

 Q1. A hydraulic press has a ram of 15 cm diameter and plunger of 1.5 cm. It is required to lift a mass of 1000kg. The force required on plunger is nearly equal to (a) 100N  (b) 1000N (C) 10000N (d) 10N Ans (a) By pascal law: F1/A1 = F2/A2 F1/3.14(1.5)^2/4 = 1000×10/3.14(15)^2/4                               F1 = 100N...................................................................................................(Ans) *3.14 is value of pi π *F2= 1000×10= m×g= mass×acceleration due to gravity(9.8)  *A1= 3.14(1.5)^2/4 = πd 2 /4 = area of circle  *A2= 3.14(15)^2/4 =  πd 2 /4 *15 cm diameter value of circle at point2 *1.5 cm diameter value of circle at point1