3.3.3 Motion Through a Fluid: Drag Force and Terminal Speed

Question 1

Motion Through a Fluid: Drag Force and Terminal Speed

Answer 1

• The drag force is a frictional force that resists the motion of objects through a fluid. For objects in air at moderate speeds,is a good approximation of the drag force.
• A falling object is not subject to air drag when its velocity is very small and linearly increasing.
• As the velocity of a falling object increases, Fdrag increases to a maximum value of mg. When this occurs, the object reaches its terminal velocity, .

Question 2

Which of the following statements regarding drag force and terminal speed is not correct?

Answer 2

The drag coefficient is a unitless, proportionality constant, of the drag force that depends on the size, shape, weight, and texture of the object.

Question 3

Which of the following statements is not correct?

Answer 3

• An example of drag force is the force of air on a cyclist riding into the wind.
• The drag force is a frictional force that resists the motion of objects through a fluid.
• Unlike kinetic friction, the drag force does not depend on the normal force.
• All the answer choices are correct

Question 4

1/2 CrAv^2

Which of the following statements regarding this equation is not correct?

Answer 4

The term v is the volume of the fluid and its unit is meters cubed.

Question 5

The drag force, Fdrag, depends on several variable factors. Which of the following factors does not affect the drag force on an object?

Answer 5

The mass of the object, m, moving through a fluid.

Question 6

The diagram shows an object falling to the ground. Given that the drag force is equal to the force of gravity, which of the following statements is not correct?

Answer 6

When the drag force equals the force of gravity, the object will come to a halt.

Question 7

A billiard cue ball, a baseball, a handball, and a yellow tennis ball all have the same diameter and cross-sectional surface area. They are all thrown through the air with equal initial velocity. Which ball will have the smallest value of C, the drag coefficient?

Answer 7

The tennis ball.

Question 8

Terminal velocity, vT, is the speed at which the drag force on an object equals its weight. Which of the following is the correct equation for vT?

Answer 8

vT = sqrt (2mg/crA)

Question 9

The attached force diagram shows a parachutist who has just stepped out of a helicopter. Her weight (mg) is the only force. Which of the following statements is not correct?

Answer 9

As long as she continues falling, the parachutist’s velocity will steadily increase.

Question 10

Which of the following statements is not correct?

Answer 10

The formula Fdrag ∝ v is a very precise and accurate measure of drag force