Tagged Questions
1
vote
1answer
26 views
How to calculate air resistance of penny dropped from Empire State Building?
If a penny is dropped from the Empire State Building, then its speed, without taking air resistance into consideration, is
$\sqrt{\left(32\frac{\textrm{ft}}{\textrm{s}^2}\right)(1454\textrm{ ...
3
votes
1answer
44 views
Why doesn't this equation for orbital motion change with position in the orbit?
The question and answer are on pg.8-10 of this PDF:
At first, I went through it, thinking nothing of it. But then, I wondered: "What if we picked a final state in which the space junk was NOT at ...
0
votes
1answer
68 views
Vector cross product of $\mathbf{r}$ and $\ddot{\mathbf{r}}$ in polar coordinates
I'm struggling with the following question:
Question 6 A planet of mass $m$ moves under the gravitational attraction of a central star of mass $M$. The equation of motion of the planet is
...
0
votes
2answers
55 views
Constant of gravity in earth fixed coordinate system
I have this problem:
If the constant of gravity is measured to be $g_0$ in an earth fixed
coordinate system, what is the difference $g-g_0$ where $g$ is the
real constant of gravity as ...
6
votes
4answers
133 views
Integrating radial free fall in Newtonian gravity
I thought this would be a simple question, but I'm having trouble figuring it out. Not a homework assignment btw. I am a physics student and am just genuinely interested in physics problems involving ...
1
vote
1answer
76 views
Pendulum in an elevator
Suppose we have a pendulum tied to the ceiling of an elevator which is at rest. The pendulum is oscillating with a time period $T$, and it has an angular amplitude, say $\beta$. Now at some time ...
0
votes
2answers
50 views
Escape velocity to intersection of two gravitational fields
Find the minimal velocity needed for a meteorite of mass $m$ to get to
earth from the moon. Hint: the distance between the center of earth
and the center of moon is $\approx 60 R_E$, and the ...
3
votes
1answer
62 views
Tension of rope in the gravitational field of earth
Two balls of mass $m$ each one are connected with mass-less rope with
the same length as the radius of earth. The system is in free fall.
Prove that the tension of the rope when the nearest (to ...
1
vote
2answers
79 views
The potential and the intensity of the gravitational field in the axis of a circular plate
Calculate the potential and the intensity of the gravitational field at a distance $x> 0$ in the axis of thin homogeneous circular plate of radius $a$ and mass $M$.
Could anybody describe how to ...
0
votes
0answers
30 views
Understanding Kepler's $2^{nd}$ law in terms of angular momentum conservation
A) Explain how Kepler's $2^{nd}$ law - "The radius vector from the Sun to a planet sweeps out equal areas in equal time intervals" - can be understood in terms of angular momentum conservation.
I ...
0
votes
2answers
77 views
How to calculate time for ball to reach plane while considering mass, gravity and wind resistance?
The scenario that I'm having is such that a ball of radius $15mm$ is thrown from a location point $\vec{p}=(2, 5, 2)$ in a direction of $\vec{d}=(3, 0, 4)$. The initial velocity is $30m/s$. There were ...
0
votes
3answers
100 views
Solve for Initial Velocity of a projectile given Angle, Gravity, and Initial and Final positions?
I've found equations http://www.physicsclassroom.com/Class/1DKin/U1L6a.cfm for solving everything (and rearranged to solve everything) to do with projectile motion EXCEPT this, even though it should ...
1
vote
3answers
115 views
Projectiles and escape velocity
Q: The escape velocity for a body projected vertically upwards from the surface of earth is 11 km/s. If the body is projected at an angle of $45^\circ$ with vertical, the escape velocity will be?
...
0
votes
1answer
65 views
What Speed Would an object need to leave the earth at to reach L1? [closed]
Let's say the Earth is an airless sphere. What speed would an object weighing 1 kg need to leave the surface at in order to get to and be motionless at L1, where the Moon's gravity becomes stronger ...
0
votes
0answers
58 views
How much energy would it take to move the asteroid that has been implicated in the dinosaur extinction by a few centimeters? [closed]
One of the greatest mass extinctions occurred about 65 million years ago, when, along with many other life-forms, the dinosaurs went extinct. Most geologists and paleontologists agree that this event ...
2
votes
2answers
98 views
Where are we : On level ground or on a ramp - moving in a train?
Let's say we are traveling in a train. The path has two parts: one at ground-level and the other moving up on the ramp. The ramp has an inclination of $\arctan\frac{a}{g}$ with the horizontal, where ...
1
vote
4answers
152 views
How to get the angle needed for a projectile to pass through a given point for trajectory plotting
I am trying to find the angle needed for a projectile to pass-through a given point.
Here is what I do know:
Starting Point $(x_0,y_0)$
Velocity
Pass-through point $(x_1, y_1)$
I also need to ...
1
vote
1answer
64 views
Distance traveled in a simple two body problem [duplicate]
I'm trying to program an $N$-body simulation and I'd like to be able to test it with a known solution to a simple, two-body problem. I've looked at multiple sources, but I just don't know how to apply ...
2
votes
1answer
189 views
How can a satellite's speed decrease without its orbital angular momentum changing?
I have no idea what the answer is. I'm supposed to answer it within 3-4 sentences.
0
votes
1answer
86 views
Lagrange L4 L5 points and perifocal plane
I have 2 satellites at the L4 and L5 points and these are watching an object. Each satellite provides the angle to the object from its own position from a line parallel to the $\text{x-axis}$ of ...
3
votes
4answers
577 views
Why does an object thrown parallel to the ground eventually fall down?
Suppose an object is thrown parallel to the ground. The gravity acts downward (ie. perpendicular to the direction of motion of the object). The work done by gravity on that object will be given by :
...
1
vote
1answer
99 views
Idealized trajectory from sloped surface
I am a GIS programmer implementing a visualization.
I am modeling the idealized trajectory of a particle ejected from a volcanic vent using:
$$\text{distance} = \frac{(v^2 \times ...
4
votes
1answer
107 views
Potential Energy tends to infinity on the N-Body Problem
I need help to solve this problem related with the N-Body problem, i dont understand quite well what I need to define or to express in order to solve it.
We assume a particular solution to the N-Body ...
4
votes
2answers
108 views
What was the muzzle velocity of a home made gun launch strait in the air if air time was 8.2sec?
I built a potato gun and wanted to calculate the muzzle velocity. I remember from physics that I could run the numbers by calculating time from launch until landing. After pointing strait into the air ...
0
votes
1answer
80 views
What is the orbital motion where both foci are located at one point?
What is the orbital motion where both foci are located at one point? I know that an ellipse orbit is motion with two distinct foci.
1
vote
1answer
125 views
How much runway does the space shuttle need to land?
A textbook question proposes the following scenario:
NASA needs to plan emergency landing sites for the Space Shuttle (RIP). There are a number of things to consider. The shuttle touches down no ...
3
votes
1answer
230 views
Finding the diameter a parachute must be to land a probe on Mars at specific speed
Hi I'm trying to solve this textbook example but I don't know where to begin;
NASA has decided to send an experimental probe to Mars. Its weight on earth is $40 kg_f$. When the probe is near ...
1
vote
1answer
451 views
Friction due to air drag at high speeds
I am trying to set up this problem, but I am not sure how to go about doing so. (From University Physics, Young & Freedman):
You throw a baseball straight up. The drag force is proportional to
...
1
vote
1answer
391 views
Needed Energy For Lifting 200 kg weight
I'd like to learn how much energy I need to lift a 200 kilograms weight on normal earth conditions?
For example how much electric power do we need?
I'm not a physicist and not a student and this ...
0
votes
1answer
346 views
Satellite Orbital Period [closed]
I know I can calculate the period of a satellite orbit by Kepler's third law, but somehow it does not work out.
The sattelite is 20200km from surface of the earth.
$r=$orbits radius=earths ...
0
votes
1answer
82 views
Newton's Gravitational Law [closed]
Is this correct..?
Gravitational constant, $G = 6.67 × 10^{-11} Nm^2kg^{-2}$
Mass of Sun, $M = 1.99 × 10^{30} kg$
Mass of Earth, $m= 6.02 × 10^{24}kg$
Distance between Sun and Earth, $R= 1.5 × ...
2
votes
2answers
112 views
Force to use in harmonic oscillation through the inside of a planet
I am to find an equation for the time it takes when one falls through a planet to the other side and returns to the starting point. I have seven different sets of values - mass of object falling, mass ...
0
votes
0answers
19 views
Capsule traveling through a planet, find time for return [duplicate]
Possible Duplicate:
If it was possible to dig a hole that went from one side of the earth to the other
A corporation is building attractions in outer space, in which they drill tunnels ...
0
votes
1answer
193 views
Time taken for object in space to fall to earth
The Problem
For a small mass a distance $R_i$ away from the center of the Earth, how long would it take for the object to fall to the surface of the Earth, assuming that the only force acting upon the ...
1
vote
1answer
146 views
How do I factor in multiple forces into these Newtonian mechanics equations?
Say a person is walking along.
He then jumps.
The person weighs $25$kg (irrelevant?).
Just after jumping, his velocity is 5m/s (positive is taken as up).
Gravity is taken as ...
1
vote
1answer
96 views
Gravitation and equilibrium (…and similar problems)
One problem that I'm having trouble with (as opposed to the other):
The Messenger is a probe that orbits Mercury $700 \rm km$ from the surface. What is the tangential velocity it should be ...
0
votes
0answers
68 views
Trajectory of a photon due to a constant/uniform gravitational force [closed]
I have a small problem of physics linked to a basic ray tracing algorithm. My problem is the following :
At $t = 0$, a photon at the position $(x_0 = x_\text{min},y_0 = y_\text{min})$ with the ...
0
votes
2answers
99 views
Calculating kinetic energy?
Would this be a valid equation to calculate kinetic energy created from a drop from a height:
$$E_{kinetic} ~=~ v_{vertical}tmg$$
Velocity multiplied by time gives distance. Distance multiplied by ...
0
votes
2answers
165 views
Dynamics - Beginner question
I am trying to understand this question, but I keep coming to a dead end:
Two identical rectangular masses rest on top of one another, the top is tied to a wall on the left, while the one on the ...
2
votes
2answers
414 views
Gravitational field with cavity removed
I'm just struggling a little with this question:
A uniform sphere, of radius $R$, contains a spherical cavity of radius $R/4$, whose centre is $3R/8$ from the surface. The diameter passing through ...
0
votes
1answer
108 views
What would be the path of the earth seen by the astronaut in the lunar sky? [closed]
An astronaut camps on the moon for a period of one month as per the earth’s calendar.
What would be the path of the earth seen by the astronaut in the lunar sky?
(A) The earth remains approximately ...
0
votes
3answers
1k views
Centripetal/Gravitational Force
Suppose a satellite is orbiting the Earth. The gravitational and centripetal force supposedly point towards the Earth. Therefore, the net force is towards the Earth. Since the satellite doesn't fall ...
-4
votes
2answers
143 views
Gravitational attraction [closed]
The mutual force with gravitational attraction between two masses is 500N.
a. If the masses are moved 5 times as far apart, what is the new mutual force of gravitational attraction?
b. If the masses ...
