Two cylindrical logs of the same texture are placed on the construction site. The base radius of A root is twice that of B root, and the length of B root is twice that of A root. The captain asked Master Wang to weigh the weight of the two logs. Master Wang only weighed 40 kilograms for the first root, and then said to the captain, "You can know the weight of the second root even if you don't weigh it." How much does the second log weigh?
工地上放着两根质地相同的圆柱形木料，甲根底面半径是乙根的2倍，乙根的长度是甲根的2倍．队长让王师傅称一称这两根圆木有多重，王师傅只称得甲根重40千克，然后跟队长说："乙根不称也知道有多重．"乙根圆木有多重？
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<result>20</result>