Question

The diagram below (Fig.) shows a uniform bar supported at the middle point $O$. A weight of $40gf$ is placed at a distance $40cm$ to the left of the point $O$. How can you balance the bar with a weight of $80gf$?

• A. By placing the weight of $80gf$ at a distance $10cm$ to the right of the point $O$.
• B. By placing the weight of $40gf$ at a distance $20cm$ to the right of the point $O$.
• C. By placing the weight of $160gf$ at a distance $10cm$ to the right of the point $O$.
• D. By placing the weight of $80gf$ at a distance $20cm$ to the right of the point $O$.

Answer 1

The correct option is D By placing the weight of $80gf$ at a distance $20cm$ to the right of the point $O$.

Given that 40 gf is applied at a distance of 40 cm from point O. Hence moment of force is $40\times 40=1600gfcm$. Hence this moment of force must be balanced by 80gf of force. After equating we get $1600gfcm=x\times 80gfcm$
$x=1600/80cm$
$x=20cm$.
Hence 80 gf must be applied at a distance of 20 cm. This is all because of clockwise and anticlockwise moments are equal.