Question

A uniform meter ruler of weight $0.1kgf$ is balanced on a fulcrum at $40cm$ mark by suspending a weight, $w$ at the $20cm$ mark . What is the value of $w$?

• A. $20gf$
• B. $500gf$
• C. $300gf$
• D. $50gf$

Answer 1

The correct option is D $50gf$

We know that the weight of the ruler will act at the centre i.e., at the 50 cm mark.

Moment of the ruler about the fulcrum
$=Force\times perpendiculardistance$
$=0.1kgf\times 10cm=1000gfcm$ (Clockwise).
Moment of weight, w about the fulcrum $=w\times 20=20wgfcm$ (Anticlockwise).
By principle of moments,
Clockwise moments = Anticlockwise moments
100 gf $\times$ 10 cm = w gf $\times$ 20 cm
w = 50 gf.

Therefore, the value of weight, w = 50 gf.