A hollow iron pipe is 21 cm long and its external diameter is 8 cm. If the thickness of the pipe is 1 cm and iron weights 8g/cm cube, then find the weight of the pipe.
Choose the correct choice from the following:
A) 3.696 kg  B) 3.686 kg  C) 2.696 kg  D) 2.686 kg  E) None of these
Explanation:   In this type of question, we need to subtract external radius and internal radius to get the answer using the volume formula as the pipe is hollow. Oh! line become a bit complicated, sorry for that, lets solve it.   External radius = 4 cm   Internal radius = 3 cm [because thickness of pipe is 1 cm]   Volume of iron =πr2h=22/7∗[42−32]∗21cm3   =22/7∗1∗21cm3=462cm3   Weight of iron = 462*8= 
<gadget id="calculator">462*8</gadget>
<output>3_696</output>
3696 gm= 3.696 kg   Option 3.696 kg
<result>A</result>
A hollow iron pipe is 21 cm long and its external diameter is 8 cm. If the thickness of the pipe is 1 cm and iron weights 8g/cm cube, then find the weight of the pipe.