We have,
Cylindrical vessel Diameter =d=42cm.
Then,
Radius=r=21cm.
Height h=21cm.
We know that,
Volume of cylinder
Volume(1)=πr2h
=πd24×d
=πd34
Now, Dimension of smaller cylinder
Volume=πr2h
=πd24h
Now, According to given question,
Volume(1)=2×volume
πd34=2×(π×42×42×21)4
d3=42×42×42
d3=423
d−42cm.
Hence, the diameter is 42 cm.