Answer :

Correct answer is : 2.82

Steel rectangular plate with dimensions = 75 mm × 125 mm × 20 mm, t = 2 minutes

Modulus of steel plate $=\frac{75\times 125\times 20}{2\left[(75\times 125)+(20\times 125)+(75\times 20)\right]}=7mm$

Cylinder H = 50 mm, D = 50 mm.

Modulus for cylinder shape $=\frac{D}{6}=\frac{50}{6}=8.33mm$

Time ∝ (Modulus)²

$\Rightarrow \frac{Timeofcylinder}{Timeofplate}={\left(\frac{Moduleofcylinder}{Moduleofplate}\right)}^2$

$\Rightarrow \frac{t}{2}={\left(\frac{8.33}{7}\right)}^2$

∴ t = 2.83 minutes