In first situation.
Radius = r1, height = h1 and volume = v1
In second situation,
Radius =2r1, height = h2 and volume = v2
In the volume is fixed, then
v1 = v2
⇒ (1/3)πr21h1 = (1/3)π(2r1)2h2
⇒ h1 = 4h2
∴ h2 = h1/4
Therefore, height of the the cone will be one-fourth of the previous height.