<PRE><B>Question 28912</B>
A man places one end of a crowbar 5.5 feet long under a rock. At a 4.5 inches from the rock, he places a stone to use as a fulcrum. If he uses a force of 160 pounds at his end of the crow bar, he just raises the rock. How much does the rock weigh?
LET AB BE THE CROW BAR END A IN THE HAND AND END B UNDER THE ROCK.
AB=5.5 FEET = 66 INCHES
LET C BE THE FULCRUM POSITION 
BC=4.5 INCHES.
HENCE AC = AB - BC =66-4.5=61.5 INCHES
FORCE AT A =160 POUNDS
TAKING MOMENTS ABOUT FULCRUM,WE GET 
160*AC=ROCK WEIGHT*BC
ROCK WEIGHT =160*AC/BC=160*61.5/4.5=2186.67 POUNDS
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