Question

We learned in mechanics that in the absence of air resistance, all objects near Earth’s surface fall with the same constant acceleration g = 9.8 m/s 2 . Yet as a student I once dropped a wadded-up tissue from the top of the Eiffel Tower and watched it take minutes to fall 300 m to Earth. (I retrieved it from the riverbank and put it in the poubelle.) In fluids, such as air or water, frictional drag forces grow larger as speed increases: often Fdrag ∝ v (or Fdrag ∝ v 2 if turbulence is present). The result is that once a falling object reaches terminal velocity, where the upward drag force balances the downward gravitational force, the object no longer accelerates: it continues downward at constant speed. (a) If an object falling downward at speed v feels an upward drag force Fdrag = bv (where b is some constant that depends on the object’s size and shape and the fluid properties), what is its terminal speed vterm? (Write vterm in terms of m, g, and b.) (b) Using your expression for vterm, explain how it makes sense that a ping-pong ball dropped from a rooftop takes longer to fall to Earth than a steel ball of the same size and shape.

Answer #1

The terminal speed will be attained when the net force on the object becomes zero i.e the downward force of weight is balanced by the upward drag force.

b) As can be seen from above relation terminal speed is directly proportional to the mass of the object. Since the mass of steel ball is more than ping- pong ball of the same size the terminal speed of steel ball is more and hence it takes less time to cover the distance and ping - pong ball has less terminal speed so it takes more time to cover the same distance.

In the absence of air resistance, all objects dropped near the
Earth’s surface accelerate at the same rate. If two similar objects
are dropped, one a short time interval Δt after the other:
a) What can you say about the relative speeds of the two objects
at any instant after both objects are in free fall? In other words,
will ball B be moving faster, slower, or at the same speed as ball
A? Why?
b) What happens to their...

Air drag is like a friction force in that it acts to resist
motion of an object through the air. Consider an object falling
through the air and select all the correct statements that could
describe the motion of the object while it is falling.
1.Since there are always forces acting on the object, it is
constantly accelerating (not = 0)
2.The sum of forces on the object could be zero despite
falling
3.The speed of the falling object will...

We are currently learning about drag forces and air resistance.
My professor asked us to "argue to the v 2 dependence for turbulent
flow by considering a falling object of cross sectional area A,
speed v and mass M. Assume the air molecules have mass m, density
ρ. You can then derive the force on the object in terms of A, ρ and
v. " she gave us these hints:
turbulent flow formula: F = 1/2 πρCd*r^2 *v^2
Air molecules...

Write clearly & legibly. Show all work. Use units.
Assume g = 10/m/s2. Ignore air resistance. Due next Monday as a
handwritten hardcopy at period start.
A 100 g ball is held in a person’s hand. The person
throws the ball straight up in the air.
During the throw, the person accelerates their hand
upward from rest to an upward velocity of 7.5 m/s after an upward
displacement of 75 cm. Assume constant acceleration of the hand
during the upward...

do all five questions
Question 1
20 pts
Ignoring the effects of air resistance, if a ball falls freely
toward the ground, its total mechanical energy
Group of answer choices
increases
remains the same
not enough information
decreases
Flag this Question
Question 2
20 pts
A child jumps off a wall from an initial height of 16.4 m and lands
on a trampoline. Before the child springs back up into the air the
trampoline compresses 1.8 meters. The spring constant...

Do all five questions
Question 1
20 pts
Ignoring the effects of air resistance, if a ball falls freely
toward the ground, its total mechanical energy
Group of answer choices
increases
remains the same
not enough information
decreases
Flag this Question
Question 2
20 pts
A child jumps off a wall from an initial height of 16.4 m and
lands on a trampoline. Before the child springs back up into the
air the trampoline compresses 1.8 meters. The spring constant...

• Cooper is standing on a 45◦ hill. He kicks a rock (m = 1kg)
with a force of F = 50N down the hill. His foot is in contact with
the rock for 0.1 seconds. How fast will the rock be moving after 5
seconds? How long does it take for the rock to travel 100 meters?
Ignore pesky friction and rotation.
• When an object is falling, it is said to be at terminal
velocity if it is...

Two boxes are stacked, with box B placed on top of box A. If box
A is pushed such that both boxes move with a decreasing speed, is
there any friction on either box?
(a) Kinetic friction on box A and no friction on box B (b)
Kinetic friction on box A and static friction on box B
(c) Kinetic friction on box A and kinetic friction on box B (d)
Static friction on box A and kinetic friction on...

answer all questions
3.13.6
Question 110 pts
A 319 kg motorcycle is parked in a parking garage. If the car has
35,494 J of potential energy, how many meters above ground is the
car? Report your answer to 1 decimal place. Please do not include
units or the answer will be marked incorrect.
Flag this Question
Question 210 pts
A box sitting on the top of a hill has 252 J of potential energy.
If the hill is 279 meters...

ADVERTISEMENT

Get Answers For Free

Most questions answered within 1 hours.

ADVERTISEMENT

asked 28 minutes ago

asked 43 minutes ago

asked 46 minutes ago

asked 1 hour ago

asked 2 hours ago

asked 2 hours ago

asked 2 hours ago

asked 2 hours ago

asked 4 hours ago

asked 4 hours ago

asked 4 hours ago

asked 4 hours ago