Chapter 4.1, Problem 1PP

To determine

To Specify:The system.

To Draw:A motion diagram and free body diagram.

Answer to Problem 1PP

When the skydiver is movingdownwards faster, air resistance acting on him increases and the force of air resistance becomes equal to that of gravitational force. Hence the skydiver continues downwards with a constant velocity.

Explanation of Solution

Introduction:

When a skydiver jumps out of an airplane, there are two forces acting on him: the Earth’s gravitational force pulling him straight down, and the air resistance. Air resistance pushes the skydiver in the upward direction. Air resistance increases as the skydiver’s speed increases. Thus, when a skydiver starts dropping from a plane and moving slowly, gravitational force is stronger than the air resistance and he speeds up and accelerating towards the Earth. As he is moving faster, air resistance acting on him also increases and the force of air resistance become equal to that of gravitational force. Since the air resistance is acting in upward direction (opposing the downward motion of the skydiver) and the gravitational force is in the downward direction (accelerating the skydiver towards the earth), their sum becomes zero. So, the skydiver will not accelerate anymore and continues downwards with a constant velocity so that she lands safely.

  

Figure:1

Figure 1 shows the system and a motion diagram and free body diagram of a skydiver falling downward through the air at constant velocity. The skydiver and his surrounding media represents the system. The velocity is in the downward direction since a skydiver move downwards. At certain point, the force of air resistance which is acting in the upward direction and the force due to gravity becomes equal. Hence, the net force is equal to zero and the skydiver will not accelerate any more (that is acceleration is zero).