Question

When a parachutist jumps from an airplane, he eventually reaches a constant speed, called the terminal velocity. This means thatSelect one:a. the force of air resistance is equal to zero. b. the effect of gravity has died down.c. the effect of gravity increases as he becomes closer to the ground.d the acceleration is equal to g.e. the force of air resistance is equal to the weight of the parachutist.

Answer 1

When an object moves at constant speed, the net force acting on that object is equal to 0:

`\Sigma\vec{F}=0`

Two forces act over a parachutist while falling: the force of gravity (weight) and the air resistance. Those two forces have opposite directions, we can consider that the air resistance is positive because it points upwards, and the weight is negative because it points downwards:

`\begin{gathered} \Sigma F=F_{\text{air}}-F_{\text{gravity}}=0 \\ \Rightarrow F_(air)=F_(gravity) \end{gathered}`

Then, when the parachutist reaches the terminal velocity, the force of air resistance is equal to the weight of the parachutist.

Therefore, the answer is option e:

`\begin{gathered} e) \\ \text{The force of air resistance is equal} \\ \text{to the weight of the parachutist.} \end{gathered}`