Moments and balance — return questions

1. give / calculate / state

A uniform metre rule of weight 1.0 N balances on a pivot at its 50 cm mark. A 0.60 N weight hangs at its 20 cm mark. (a) Give one everyday example of the turning effect of a force. (b) Where must a 0.90 N weight hang on the other side to balance the rule? Give the centimetre mark. (c) Calculate the upward force of the pivot on the balanced rule. (d) State the two conditions for the rule to be in equilibrium. (e) Supplement. A 0.15 N weight is then hung at the 90 cm mark, with the 0.90 N weight still in place. To which mark must the 0.60 N weight be moved to balance the rule again? (f) Supplement. Explain how your readings from (b) and (e) show that there is no resultant moment on the balanced rule.

(a) Everyday example

(b) Position of the 0.90 N weight

(c) Force of the pivot

(d) Conditions for equilibrium

(e) Supplement: new position of the 0.60 N weight

(f) Supplement: no resultant moment

2. state / describe / explain

(a) State what is meant by the centre of gravity of an object. (b) Describe how to find the centre of gravity of a flat piece of card with an irregular shape. (c) An empty plastic bottle falls over easily, but with a little water in its bottom it is hard to knock over. Explain why.

(a) Centre of gravity

(b) Finding it for a card

(c) The bottle