Question

Figure below shows a uniform plank of weight 20N and length 1.0m balanced by a 0.5kg mass at a distance x from the pivot point O.

1. Determine the value of X
2. When the block is completely immersed in water the pivot O must shift by 0.05 m to the left for the system to balance. The density of water is 1000kgm^-3
   Determine:
   • The upthrust U on the block.
   • The volume of the block. 

Answer 1

1. 20(0.5 -x) = 5x
   x = 0.4m
2.   
   • F x 0.45= 20 x 0.05
     F = 2.222
     U = 5 - 2.222
     U = 2.778N
      
   • U = pVg
     1000 x 10 x v = 2.778
     V= 2.778 x 10^-4m³