What is the terminal velocity of a bullet falling back to earth when shot straight up?

Question

Thanks for replies - so many people reply with so many different answers.
I don't think the correct answer was given to a bullet's terminal velocity (let's say at sea level shooting).
If a human falls at ~135 mph - want is your average 150-200 grain bullet fall at?

Answer 1

Afanasijs is correct. Ignoring air resistance, which is small on a streamlined bullet, the only force acting upon the bullet is gravity. It would slow it down during the ascent and then accelerate it during the descent. Since there are no other forces, up would equal down.

Answer 2

This Site Might Help You.

RE:
What is the terminal velocity of a bullet falling back to earth when shot straight up?

Answer 3

Actually the terminal velocity of a human is more like 120MPH this is about 54 m/s while that of a bullet seems to be anywhere from 100~400m/s [223 mi/hr to 895 mi/hr] depnending on the size and mass of the slug. (Note the high end is for a 14" Naval gun!)
http://www.physicsforums.com/archive/index.php/t-14560.html

You aren't getting precise answers because this is a _very_ complicated questions. Read some of the web sites found at the link below. This calculator needs 18 variables to calculate the trajectory of a bullet: http://home.pacbell.net/aew50/trajectorydata.htm

Some of the sites use the reasoning, since the terminal velocity of a sky diver is about 120 mi/hr, a streamlined, very dense bullet will have a much greater terminal velocity, maybe around 300 or 400 mi/hr.

So, small "bullets" probably fall at 200 to 400 miles per hour, and very large artillery shells fall at around 900 miles per hour.

Terminal Velocity of a Bullet: http://linkwrap.com/4258

Answer 4

The bullet's velocity is altered by the gravity such that it decreases at a linear rate. Eventually, it reaches a maximum height where the velocity is zero, then it falls back with the same change in velocity. Theoretically, the velocity will be the negative of the initial velocity (same speed, opposite directions). However, with some air resistance, the bullet's rate will be slowed faster go both up and down, so it will land with a lower speed, although probably not much lower than the theortical value as bullets are fairly aerodynamic.

Hope that helps.

Answer 5

In a vacuum, the bullet would leave the barrel of the gun (at some height from the ground (h)) and at some velocity (x). The bullet would travel upwards turn around and fall back due to gravity. At the instant the bullet was at the same height as the barrel it left (h) it will be at the exact same speed it was when it left the barrel. Below that it would actually be faster.

Not in a vacuum many factors have to be takne into account: air pressure, humidity, air friction...that's a tough one.

Answer 6

Maximum Falling Velocity

5/24/2004


name Peter
status educator
age 60s

Question - Isn't it true that, on earth, where no object really
falls "freely", there is a point at which the falling object finally
attains zero acceleration? That is, could you say that, in reality, a
falling object attains a maximum velocity above which it will not go?
-----------------
Peter -

What you say is true. The traditional acceleration due to gravity (9.8
meters per second per second) is assuming a vacuum. However, for short
falls, it works out well.

For longer falls, the force of gravity is eventually equaled by the force of
air resistance. At this time the speed remains constant. As you are likely
aware, in order to have a change in velocity, an unbalanced force is
required.

The "terminal velocity" is determined by the shape of the object. Sky
divers can speed up and slow down by changing the shape they present to the
relative wind (the air going by them). Ultimately, they open their
parachute and greatly increase the for of the air resistance... (luckily!)
slowing them down considerably.

Larry Krengel
=====================================================
Yes, there is a maximum velocity an object will reach (called the terminal velocity),
but gravity will always be pulling on it at an acceleration around 9.81 m/sec^2. What
is causing the terminal velocity is a resistance force that is caused be the wind, or
the friction of moving through air. The fall is a matter of balancing forces. The
force of gravity pulling you down is counterbalanced at some point due to the force of
the wind resistance trying to slow you down.

Hope this helps and thanks for using NEWTON.

Christopher Murphy, P.E.
=====================================================
You are absolutely correct! Gravity accelerates an object high up in the
air downward at the usual rate of 32 ft/second/second. As it accelerates,
however, the air resistance increases, roughly like speed at low speeds and
then more like the square of the speed. Finally, the air resistance exerts
an upward force exactly equal and opposite to the force of gravity. The
object will then continue to fall at that speed, which is called the
terminal speed.

For a person in free fall, the terminal speed is about 60 m/s or 135
miles/hour. When his parachute opens (hopefully), the terminal speed is
reduced to around 12 miles/hour.

Best, Dick Plano, Professor of Physics emeritus, Rutgers University
=====================================================
In "theory" the answer is yes, but the answer is not simple. The main
resisting force to a falling object is wind resistance(friction against the
flow of air) and to a much lesser extent buoyancy (the volume of air
displaced by the falling object). The former depends upon the shape of the
object which determines how and if it tumbles as it falls.
This obviously is a very complicated thing to predict. Even the buoyancy
changes if the falling object is compressible ( i.e. a balloon). So there is
a maximum speed but it is not all that simple to determine what it will be.

Vince Calder
=====================================================
Peter D. B.,
In open air, there is a maximum falling velocity due to air resistance.
When an object moves through air, the object must push the air out of the
way. In return, the air pushes back on the object. You feel air resistance
when you put your hand out the window of a fast car. The faster an object
moves through the air, the greater the air resistance. When falling,
eventually an object speeds up enough to make air resistance as large as
gravitational force. This is terminal velocity. If the object drops faster
than terminal velocity, then air resistance is greater than gravity: the
object slows down. If the object drops slower than terminal velocity, then
gravity is the greater force: the object speeds up.


Exactly what the terminal velocity is depends on the shape, size, and
density of the object. The terminal velocity of a man with an open
parachute is much slower than that of a man without a parachute. It also
depends on the material the object moves through. Terminal velocity of a
steel ball falling through water is much slower than that of a steel ball
falling through air. An object falling in a vacuum has no terminal
velocity. The only limit would be due to Einstein's relativity, a
completely different subject.


Dr. Ken Mellendorf
Physics Instructor
Illinois Central College

Answer 7

Mathematically, it would be as follows:
From the summing of forces of the bullet as a fbd:
F=mg(force of gravity)-1/2D(drag coefficient of bullet)rho(density of air, varies with altitude if you want to be precise)A(cross sectional area perpendicular to direction of motion)v^2(velocity)

or: F=mg-1/2DrhoAv^2

If you are looking at terminal felocity we should take the equation one more step by inserting ma where F is (newton's second law)

we get:

ma=mg-1/2DrhoAv^2

However we are looking for terminal velocity, so our acceleration would be zero rendering the left side of the equation to be zero. Solving for v we get:

v=((2mg)/(DrhoA))^(1/2)

you plug in the mass, accleration due to gravity, density of air, drag coefficient, cross sectional area and you can find the terminal velocity. The actuall equation is much more difficult due to the fact that gravity and air density change with altitude, this will get you close though.

Answer 8

Its terminal velocity (when it is falling down) is the velocity of the bullet JUST before hitting the ground, so its velocity at that case is equal to the velocity that it is shot from the same place (when it was shot upwards) ---------> according to the law of conservation of energy

i hope u got ur point from my explanation

Answer 9

as all falling objects they fall at the same rate of speed,62 mph

Answer 10

121 mph