This is the suggested answer for the multiple choice question in GCE O Level Pure Physics, Year 2011 November, Paper 1, Question 5.
The question asked about the forces acting on a parachutist when his parachute is fully opened and the parachutist falls toward the ground at constant speed.
The answer should be B, i.e. the upward force on the parachute is equal to the weight of the parachutist.
When a parachutist leaps out of the air plane, two forces are acting on him:
- The downward gravitational pull
- The upward air resistance that opposes his downward motion
As he falls, air resistance increases with his increasing speed but it reached a point where the air resistance equals his weight. That is when he reached terminal velocity which is the constant velocity that he continues his downward motion. Click here for more information on the science of skydiving and parachuting.