The diagram shows a uniform beam pivoted at its centre. The bar weighs 800N, and three
other forces act on it as shown. Distance x can be varied. What value of distance x would cause the beam to be balanced?

Answer:

4) B

Pivot is located in the middle. So ignore the weight of the bar.

Moments clockwise = Moments anticlockwise:

(500 x 0.2) = (0.4 x 200) + 200x

100 = 80 + 200x

x = 20 ÷ 200 = 0.1m = 10 cm