Please describe the change in velocity of someone falling from a plane before they open their parachute
At first, when the parachutist is at 0ms-1 velocity (about to fall) there is only Weight acting downwards on the person, so the resultant force is down. F=ma, therefore the parachutist accelerates downwards. Then as the velocity of the person increases, drag also increases in the opposite direction, upwards. Drag is directly proportional to velocity^2. Therefore, as drag increases upwards, and the weight of the person stays the same, the resultant force downwards decreases, and therefore acceleration also decreases downwards. Until the magnitude of the drag force is equal to that of the weight. This in turn means that there is no acceleration and the parachutist has reached terminal velocity.
PE
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