Tagged Questions
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
66 views
How to calculate offset (lifting point) from Centre of Gravity (CG) to achieve a particular angle 26° [closed]
An object is suspended at a point at a distance of XXX from Centre of Gravity with two strings. The two strings are of equal length.
What should be the distance XXX to achieve 26° angle?
1
vote
1answer
110 views
Photon on null geodesic
If given an FRW metric
$ds^2 = -dt^2 + a^2(t)[dx^2+dy^2+dz^2]$
and for the trajectory followed by a photon (null geodesic; $ds^2=0$) with affine parameter $\lambda$, know that
...
0
votes
1answer
67 views
About the work done by gravity to pull the object down to the earth surface
The following question is from an physics exercise and I know the answer and the way to solve the problem but just curious why my own way doesn't work. The question is asking "A 2500kg space vehicle, ...
0
votes
2answers
279 views
Generating artificial gravity by using rotation
If I want to design for futuristic space stations and I want to use rotation to produce
artificial gravity. One of such designs consists of a giant ring that is rotated about its centre. If it were ...
3
votes
1answer
153 views
Calculating Riemann Tensor Using Tetrad Formalism
I was trying to calculate the Riemann Tensor for a spherically symmetric metric:
$ds^2=e^{2a(r)}dt^2-[e^{2b(r)}dr^2+r^2d\Omega^2]$
I chose the to use the tetrad basis:
$u^t=e^{a(r)}dt;\, ...
3
votes
3answers
115 views
Relation between the determinants of metric tensors
Recently I have started to study the classical theory of gravity. In Landau, Classical Theory of Field, paragraph 84 ("Distances and time intervals") , it is written
We also state that the ...
3
votes
4answers
574 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 :
...
2
votes
1answer
237 views
Calculating projectile range from known maximum height and time traveled
I've been stuck on this problem for many hours and I think I'm onto the right solution but I'm uncertain about my math.
I've got a projectile that I know its maximum height and it's hang time and I ...
0
votes
0answers
54 views
Projectile Pathway [closed]
Assume you have a planet of mass $M$ and radius $R$ and have a stationary spaceship at distance $4R$ from the center of the planet.If a projectile is launched from the spaceship of mass $m$ and ...
0
votes
0answers
66 views
How to calculate the mass of the Cygnus X-1 black hole?
I have received a question about how to calculate the mass of Cygnus x-1 (black star).
Since we are able to find the the mass through this Wikipedia page I know that we can find the mass through ...
0
votes
0answers
137 views
What is the pressure in a vertical pipe that has moving fluid through it?
I have a system like this
When the valve is closed, pressure along any point along the thin tube may be found thru pgh. 1. What about when the valve is opened? 2. Does the top of the jar need to be ...
1
vote
1answer
296 views
Derivation of the self gravitational potential energy of a sphere
I have been searching on the Internet but have not found a derivation of the formula for the self gravitational potential energy of a sphere. Can someone show how to do this? I assume it involved 6 ...
1
vote
1answer
138 views
Is $w=mg$ the right way to calculate mass?
How can you find the mass of an object by using a weight and a gravitational acceleration from another planet then earth? I was given $5.8\text{ N}$ and an acceleration of $4.0\ \mathrm{m/s^2}$. The ...
2
votes
0answers
160 views
include the stretch of the spring own weight in potential energy for spring pendulum?
we are given a problem with spring with its own mass $m$. I am confused how to set up the
PE term in the Lagrangian.
Assume the spring has length of $L_{0}$ when it is laying on a table
horizontally. ...
3
votes
2answers
213 views
How to measure g using a metre stick and a ball
Can I measure the value of g using only a metre stick and a ball? I am not supposed to use a stopwatch and that has been the problem.
NOTE: I do not know if a solution exists or not.
1
vote
1answer
118 views
Determining Orbital Velocity
Is there any way to determine the orbital velocity of a point around another stationary point, if I don't know the mass of either of the points but know the force that gravity exerts and the distance ...
0
votes
0answers
181 views
The Gravity Spring [closed]
This problem examines the scenario of a tunnel drilled through the center of the Earth, and the length of time required for an object to fall through the hole and back again.
use trigonometry to ...
0
votes
0answers
89 views
Looking for the right equation that will account for drag and air density [closed]
I didn't see anything about posting homework questions so here it goes. I need to find either the velocity or acceleration or the time(all 3 eventually) for an object that is falling 1000 meters. ...
2
votes
2answers
151 views
Raising a toolbox with a rope
Suppose you use a rope to hoist a box of tools vertically at constant speed v. The rope exerts a constant upward force of magnitude F_up on the box, and gravity exerts a constant downward force (the ...
1
vote
1answer
263 views
Calculating the force of a mass bearing down on an object
I need to calculate the force of a weight bearing down on a smaller object, constraining it from expansion.
The weight bearing down has a much bigger surface area than the smaller object.
I know the ...
0
votes
2answers
412 views
Basic Free Fall Problem [closed]
So I am trying to remember my childhood doing some Physics problems, but seems that I forgot almost everything. But it's not a big thing... that's why I'm training!
My problem is pretty basic ...
1
vote
0answers
183 views
How to model an accelerometer measurements on a car wheel?
I am working on kinematically modelling an accelerometer on a car wheel.
When working on the initial conditions, I am confused whether or not I should use the gravitational acceleration since there ...
1
vote
2answers
529 views
Calculating the gravitational acceleration inside of a planet
Plant X has a radius of 5000 km and is composed of two layers.
The first inner layer ranges from the centre to 2000 km from centre, it's density is 8 kg / dm^3.
The second layer ranges from 2000 ...
3
votes
1answer
533 views
Escape velocity of a rocket standing on Ganymede (Moon of Jupiter)
I want to calculate the escape velocity of a rocket, standing on the surface of Ganymede (moon of Jupiter) and trying to leave Ganymede.
My thinking was, the kinetic energy $E_{\text{KIN}}$ must be ...
4
votes
2answers
163 views
A wonky gravitational potential and its critical points
I have tough problem I am not sure how to solve:
For this question, we are confined to a plane. Consider a gravitational field that is proportional to $\frac{1}{r^3}$ instead of $\frac{1}{r^2}$, and ...
0
votes
0answers
307 views
Two objects with masses Question help [closed]
I got this wrong on a test. Can someone explain how to get the answers? I provided the answers. I just need an explanation.
Two objects with masses of 3.10 kg and 6.90 kg are connected by a light ...
0
votes
1answer
201 views
Fluid Mechanics Problem - Ball in Reservoir
I'm having a problem starting and solving the following problem:
My attempt at the solution was to realize you need to balance the upward forces with those of the downward forces in which case you ...
1
vote
0answers
248 views
Understanding 1D Kinematics and Uniform Acceleration? [closed]
So I was given the following homework problem:
You land on an unknown planet somewhere in the universe that clearly has weaker gravity than Earth. To measure g on this planet you do the following ...
4
votes
1answer
493 views
Finding the position of a planet between two other planets of known mass and distance
Here is the question:
A planet with mass $m$ and a second with mass $M$ are separated by a
distance $d$. A third planet with mass $m_3$ happens to be midway
between $M$ and $m$. Where could ...
1
vote
2answers
246 views
What method should I use to solve for the final acceleration of a projectile being launched from the earth's surface?
What method should I use to solve for the final acceleration of a projectile being launched from the earth's surface?
The question I am working on is:
A projectile is launched vertically from ...
1
vote
5answers
478 views
Conserved quantities in generalized n-body problem
Given a collection of point-particles, interacting through an attractive force $\sim \frac{1}{r^2}$.
Knowing only $m_1a=\sum_i \frac{Gm_1m_i}{r^2}$ and initial conditions we can deduce the motion of ...
0
votes
2answers
569 views
Mechanical energy problem
Question goes: "An anvil hanging vertically from a long rope in a barn is pulled to the side and raised like a pendulum 1.6 m above its equilibrium position. It then swings to its lowermost point ...
