Moments.

The two moments must be balanced.

moment = force x perpendicular distance from pivot

Perpendicular distance from the pulley weight to pivot = 100cm - 40cm = 60cm

Now you need to use a 50g mass to balance it, to prevent the pulley from pulling the metre rule upwards.


So 60cm x 20g x 10m/s² = distance you want to find x 50g x 10m/s²

1200cm g = 50cm x distance you want to find

Distance you want to find

= 1200cm g ÷ 50g
= 24cm

Since the pulley is pulling the rule up, you have to place the 50g 24cm to the right of the pivot to push down the rule.

40cm + 24cm = 64cm

The answer should be D, not C

correct answer should be (C) because the question states that the uniform meter rule has mass of 100g. since the meter rule is uniform the mass acts at the center of the meter rule.

clockwise moments = 100 x 10 + 50 x d
anticlockwise moments = 20 x 60
equating together …
100x10 + 50d = 1200
gives d = 4
40+4 = 44

Ans: (C) 44 cm

Right, the mass of the rule. neglected that