Question

How can be rule be brought in equilibrium by using an additional weight of $40gf$?

• A. By placing the additional weight of $80gf$ at the $30cm$ mark.
• B. By placing the additional weight of $80gf$ at the $70cm$ mark.
• C. By placing the additional weight of $40gf$ at the $30cm$ mark.
• D. By placing the additional weight of $40gf$ at the $70cm$ mark.

Answer 1

The correct option is D By placing the additional weight of $40gf$ at the $70cm$ mark.

Let us find individual moments of force.Considering 40 gf and 10 cm mark then 40 gf is at a distance of 40 cm from point O. we get moment of force is equal to $40\ast 40=1600gfcm.$
Now let us consider 20 gf and 90 cm mark then 20 gf is at a distance of 40 cm to the right to O. We get moment of force as $20\ast 40=800gfcm$. Both are not equal hence not in equilibrium.As we have to balance right side as it has less moment of force we must add 800 gf cm more.GIven that we have to add 40 gf weight.$800=40\ast x$
$x=800/40=20cm.$Hence mark must be at a distance of 20 cm and it must be right to O.Therefore that mark would be 70 cm mark.