596. A cube and a sphere made of cast iron (each of volume 1000 cm³) were cast under identical conditions. The time taken for solidifying the cube was 4 s. The solidification time (in s) for the for the sphere is ________.

1. 1. 6.157 sec

   
   
   

   2. 6.154 sec

   
   
   

   3. 5.157 sec

   
   
   

   4. None of these

   
   
   

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1. View Hint View Answer Discuss in Forum

   ts = k		V		2
   		A

   
   

   tsphere = tcube	A2cube	...(i)
   	A2sphere

   
   

   4	πr3 = 1000 cm3
   3

   
   ∴  r = 6.2035 cm
   A_sphere = 4πr² = 483.597 cm²
   a³ = 1000 cm³
   ∴  a = 10
   A_cube = 6a² = 600 cm²
   From equation (i),
   

   ∴  tsphere= 4 ×	(600)2	= 6.157 sec
   	(483.597)2

   Correct Option: A

   ts = k		V		2
   		A

   
   

   tsphere = tcube	A2cube	...(i)
   	A2sphere

   
   

   4	πr3 = 1000 cm3
   3

   
   ∴  r = 6.2035 cm
   A_sphere = 4πr² = 483.597 cm²
   a³ = 1000 cm³
   ∴  a = 10
   A_cube = 6a² = 600 cm²
   From equation (i),
   

   ∴  tsphere= 4 ×	(600)2	= 6.157 sec
   	(483.597)2

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597. The solidification time of a casting is proportional to (V/A)² where V is the volume of the casting and A is the total casting surface area losing heat. Two cubes of same material and size are cast using sand casting process. The top face of one of the cubes is completely insulated. The ratio of the solidification time for the cube with top face insulated to that of the other cube is

1. 1. 25

      36

   
   
   

   2. 36

      25

   
   
   

   3. 1

   
   
   

   4. 6

      5

   
   
   

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1. View Hint View Answer Discuss in Forum

   t = K		V		2
   		A

   
   

   t1/t2 =	K		V1		2
   			A1
   	K		V2		2
   			A2

   
   

   t1	=	A²1	=	(6²a)²	=	36
   t2		A²1		(5²a)²		35

   Correct Option: B

   t = K		V		2
   		A

   
   

   t1/t2 =	K		V1		2
   			A1
   	K		V2		2
   			A2

   
   

   t1	=	A²1	=	(6²a)²	=	36
   t2		A²1		(5²a)²		35

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598. The percentage of carbon in grey cast iron is in the range of

1. 1. 0.25 to 0.75 percent

   
   
   

   2. 1.25 to 1.75 percent

   
   
   

   3. 3 to 4 percent

   
   
   

   4. 8 to 10 percent

   
   
   

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1. View Hint View Answer Discuss in Forum

   

   Correct Option: C

   

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599. The iron carbon diagram and the TTT curves are determined under

1. 1. Equilibrium and non-equilibrium conditions respectively

   
   
   

   2. Non-equilibrium and equilibrium conditions respectively

   
   
   

   3. Equilibrium conditions for both

   
   
   

   4. Non-equilibrium conditions for both

   
   
   

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   Under TTT diagram cooling rate is variable.

   Correct Option: A

   Under TTT diagram cooling rate is variable.

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600. Increase in carbon content in plain carbon steel raise its

1. 1. Ductility and UTS

   
   
   

   2. Tensile strength and malleability

   
   
   

   3. Tensile strength and hardness

   
   
   

   4. Ductility and melting temperature

   
   
   

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1. View Hint View Answer Discuss in Forum

   As carbon content increases, both tensile strength and hardness increases but ductility and toughness decreases.

   Correct Option: C

   As carbon content increases, both tensile strength and hardness increases but ductility and toughness decreases.

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