Volume of a cube of side ‘$$l$$’ and volume of a sphere of radius ‘r’ are equal. Both the cube and the sphere are solid and of same material. They are being cast. The ratio of the solidification time of the cube to the same of the sphere is
A. $${\left( {\frac{{4\pi }}{6}} \right)^3}{\left( {\frac{{\text{r}}}{l}} \right)^6}$$
B. $$\left( {\frac{{4\pi }}{6}} \right){\left( {\frac{{\text{r}}}{l}} \right)^2}$$
C. $${\left( {\frac{{4\pi }}{6}} \right)^2}{\left( {\frac{{\text{r}}}{l}} \right)^3}$$
D. $${\left( {\frac{{4\pi }}{6}} \right)^2}{\left( {\frac{{\text{r}}}{l}} \right)^4}$$
Answer: Option D
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The carbide tools operating at very low cutting speeds (below 30 m/min)
A. Reduces tool life
B. Increases tool life
C. Have no effect on tool life
D. Spoils the work piece
The type of reamer used for reaming operation in a blind hole, is
A. Straight fluted reamer
B. Left hand spiral fluted reamer
C. Right hand spiral fluted reamer
D. Any one of these
High speed steel tools retain their hardness up to a temperature of
A. 250°C
B. 350°C
C. 500°C
D. 900°C
Can any one explain this answer please.
Solidification time T= C (volume/surface area)^n
Where C is a constant depends upon the material.
And n= 2 usually.