Question

A rectangular block of dimensions $6m\times 4m\times 2m$ and of density $1.5gm/c.c$ is lying on horizontal ground with the face of large area in contact with the ground. The work done in arranging it which its smallest area in contact with a ground is, $(g=10m{s}^{-1})$

• A. $2880kJ$
• B. $1440kJ$
• C. $3800kJ$
• D. $720kJ$

Answer 1

The correct option is B $1440kJ$

m=v*density

m=$6\times 4\times 2\times 1.5\times {10}^3=72\times {10}^3$kg

when face with large area is in contact with the ground its height is 2m

Centre of mass is at a height of 1m

when face with small area is in contact with the ground its height is 6m

Centre of mass is at a height of 3m

W=$72\times {10}^4(3-1)=1440kJ$