下墮重量 in fact is Weight
Therefore, weigth is 70 x 9.81 = 686.7N
You can say Drag = Weight at terminal velocity
如果佢仲下墮緊........Normal reaction, tension等都是0
所以救生繩應能受大於686.7N的tension張力,otherwise救生繩會斷
but如果6米后下墮完,救生繩已到maximum length,即係到左救生繩maximum tension
At 6米,救生繩承受著686.7N的重量