forces - forces acting on a skydiver

Question 1

how do forces on a skydiver (SD) change with velocity?

Answer 1

• as soon as skydiver jumps out of plane, only force acting is weight. due to gravity and this force won’t change
• due to weight, SD experiences a resultant force acting downwards so accelerate towards ground
• as they fall, SD experiences friction with air molecules. this is air resistance + acts upwards
• however weight still greater than air resistance so SD continues to accelerate down
• as sky divers velocity increases, air resistance also increases
• at a certain point, air resistance balances weight
• now no resultant force so velocity stays constant.SD in terminal velocity. this velocity is extremely great and SD would die if hit ground
• at this point, SD opens parachute + surface area increase so air resistance increases
• air resistance greater than weight so resultant force acting upwards causing SD to decelerate
• as velocity decreases so does air resistance then air resistance will balance weight and resultant force will be zero. velocity will stay constant
• SD falling with lower terminal velocity, now safe to land

Question 2

describe velocity time graph for SD?

Answer 2

• only force is weight
• as they fall, air resistance acts upwards. weight greater so SD accelerates
• velocity increase = increase air resistance(AR). when AR balances weight , resultant force is zero + velocity stays constant =terminal velocity
• open parachute, SA increase + air resistance increase. air resistance greater than weight so resultant force upwards so SD decelerates. lower velocity
• velocity decrease = air resistance decrease. when air resistance balances weight, resultant force is = 0. velocity now constant so lower terminal velocity.
  SD lands