(3) 3. A balloon contains 2500m3 of air. When the air is cold, its density is 1.2kg/ m3. when heated the air expands so that some is pushed out of the hole at the bottom, and the density fall to 1.0 kg/m3. Calculate the following. i. The mass of air in the balloon when cold. (2 ) (2 ) ii. The mass of air in the balloon when hot (2) iii. The mass of air lost from the balloon during heating 4. What is the unit of a moment? A Newton (N) B Newton per metre (N/m) C Newton metre (Nm) 5. State the equation for calculating moments of a force about a point [1] [2] a 6. What is the moment of a 6 N force acting 1.5 m from a pivot? 7. The moment of a force is 24 Ncm. What size is the force if it acts 8 cm from the pivot? [2].