THE TURNING EFFECT OF FORCES
3 marks · EasyA see-saw is balanced. Child A weighs 250 N and sits 1.2 m from the pivot. Child B weighs 300 N. Both are seated on opposite sides of the pivot.
Calculate the moment produced by Child A about the pivot.
How far from the pivot must Child B sit to balance the see-saw?
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) 300 Nm
(b) 1.0 m
Common mistakes: Forgetting to rearrange the formula in (b)
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Correctly calculates moment for Child A: 250 N × 1.2 m.
M1 (b) · 1 mark · Equates moments for balance: 250 × 1.2 = 300 × d. (follow-through)
A1 (b) · 1 mark · Correctly rearranges and finds d = 1.0 m. (follow-through)
Worked solution
a) Moment = 250 N × 1.2 m = 300 Nm
b) For balance: 250 × 1.2 = 300 × d