Tagged Questions
0
votes
1answer
36 views
Another Inclined plane question
I did the FBD, and I found too many variables which are not eliminating...Moreover, I believe this question is based on kinetic and static friction. But, $\mu$ here is ambiguously defined...How Do I ...
-4
votes
1answer
42 views
Center of mass of three particles of masses 1kg, 2kg, 3kg lies at the point (1,2,3) [closed]
Center of mass of three particles of masses 1kg, 2kg, 3kg lies at the point (1,2,3) and center of mass of another system of particles 3kg and 2kg lies at the point (-1,3,-2).
Where should we put a ...
0
votes
2answers
51 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 ...
1
vote
0answers
38 views
impulse problem [closed]
The figure above shows a plot of the time-dependent force $F_x(t)$ acting on a particle in motion along the x-axis. What is the total impulse delivered to the particle?
...
0
votes
1answer
40 views
Calculating the moment inertia for a circle with a point mass on its perimeter
I want to calculate the tensor of the moment of inertia. Consider this situation:
The dot represents a points mass, in size equal to $\frac{5}{4}m$. $m$ is the mass of the homogenous circle. I'm ...
0
votes
1answer
48 views
Stopping distance of two objects with equal Kinetic Energy
I'm working on a problem regarding two objects with the same kinetic energy.
Two objects with masses of $m_1$ and $m_2$ have the same kinetic energy are both moving to the right. The same constant ...
1
vote
1answer
37 views
Finding the coffecient of restitution
A ball moving with velocity $1 \hat i \ ms^{-1}$ and collides with a friction less wall, afetr collision the velocity of ball becomes $1/2 \hat j \ ms^{-1}$. Find the coefficient of restitution ...
0
votes
1answer
26 views
Forces and angles
"The little ball with the mass of 100g has gotten stuck in a chute as depicted in the picture. What forces, and how large are they, that are acting on the ball?"
This is how I solve it:
I find ...
-1
votes
1answer
87 views
Confusions about rotational dynamics and centripetal force
I am a high school student. I am having confusions about the centripetal force and rotational motion . I have known that a body will be in rest or in uniform velocity if any force is not applied. But ...
0
votes
3answers
125 views
Why does a rod rotate?
I'm a physics tutor tutoring High School students. A question confused me a lot.
Question is:
Suppose a mass less rod length $l$ has a particle of mass $m$ attached at its end and the rod is ...
0
votes
0answers
60 views
Small oscillations [closed]
I am asked to consider a fixed homogeneous rod of length $2L$ and mass density $\rho$ It is centered around $O$. A particle with mass M is moving in the same plane. The attractive force between the ...
1
vote
0answers
27 views
Doubling the energy of an oscillating mass on a spring [closed]
From this question:
Question 1.
What do we need to change in order to double the total energy of a mass oscillating at the end of a spring?
(a) increase the angular frequency by $\sqrt{2}$.
...
2
votes
1answer
81 views
Statics of Rigid Bodies — Can there be two possible solutions?
I've been working on a question and there seem to be two possible solutions. My own solution does not match the one given in the book. However, after resolving forces and taking moments with both ...
0
votes
1answer
39 views
Finding the acceleration at an angle
"What's the maximum acceleration you can achieve in a a water-slide at a 34 degree angle (If you can't use your arms and legs)"?
This is the free-body-diagram that I drew, assuming $g = 10m/s^2$:
...
2
votes
1answer
121 views
Is there a geometrical way to obtain a relationship between these vectors?
Suppose we have a setup like this. Here $a_1,a_2,b_1,b_2$ are acceleration magnitudes($b_1,b_2$ being relative) and $P,Q,R,S$ are not pulley/blocks but are points on the rope. If I use a geometrical ...
1
vote
1answer
46 views
kinetic energy of the stone
Suppose we have a man traveling in an open car (roof open) with speed $v$ towards right (man faces right). He throws a stone (mass $m$) towards right, in his frame-forward with speed $V$.
In the ...
2
votes
0answers
67 views
Classical scattering of two particles by a Yukawa potential
A point-like particle $A$, coming from minus spatial infinity, heads at another one, $B$, with an impact parameter of $b$.
Initial momenta are $p_A$ and $p_B=0$.
They repel each other via a Yukawa ...
1
vote
1answer
46 views
Measure density with the help of buoyancy
I am trying to derive a formula to calculate the density of a irregulary shaped object.
I can measure the (false) weight of the object in pure air (of known density), and the (false) weight of the ...
1
vote
1answer
76 views
Choosing the right point when calculating moments
A body is composed of two straight pins that are joined at a right angle. They have lengths $a$ and $b$ and the mass per unit length is $\rho$. When the body is balanced on a flat surface, as shown, ...
-1
votes
1answer
43 views
Leaning sticks on a horizontal surface [closed]
A body is composed of two straight pins that are joined at a right angle. They have lengths α and β and the mass per unit length is ρ. When the body is balanced on a flat surface, as shown, how large ...
-2
votes
1answer
159 views
Work done to tighten a screw [closed]
We use a wrench to turn nuts on bolts because they require less force. Consider a hexagonal nut 1 cm in diameter. We can tighten this nut with one of two wrenches, wrench A with lever arm 10 cm and ...
3
votes
1answer
390 views
Differences of behaviour of a particle in a box in quantum theory between that in classic physics
Can anyone help me enlist 3 major differences between the quantum and classical physics of the behaviour of a particle in a box? I would like some insight into the differences without solving PDEs ...
1
vote
3answers
87 views
Condition for closed orbit [closed]
I'd like to know when an orbit is closed. I know that, to have a closed orbit, there is a ratio that must be a rational number, but I don't know other things..
0
votes
0answers
93 views
Small oscillations: diagonal matrix [closed]
I'm solving an exercise about small oscillations.
I name $T$ the kinetic matrix and $H$ the hessian matrix of potential.
The matrix $\omega^2 T- H$ is diagonal and so find the auto-frequencies is ...
-1
votes
1answer
76 views
Find generating function $F_1$ for canonical trasformation
I'd like to know the steps to follow to find the generating function $F_1(q,Q)$ given a canonical transformation.
For example, considering the transformation
$$q=Q^{1/2}e^{-P}$$
$$p=Q^{1/2}e^P$$
...
2
votes
1answer
55 views
Solution of motion in hamiltonian formalism
I have these canonical equations:
$$\dot p = - \alpha pq$$
$$ \dot q =\frac{1}{2} \alpha q^2$$
I have to find $q(t)$ and p$(t)$, considering initial conditions $p_0$ and $q_0$.
I thought to simply ...
2
votes
1answer
157 views
Find the Hamiltonian given $\dot p$ and $\dot q$
I have these equations:
$$\dot p=ap+bq,$$
$$\dot q=cp+dq,$$
and I have to find the conditions such as the equations are canonical. Then, I have to find the Hamiltonian $H$.
To answer to the first ...
1
vote
2answers
333 views
Problem of Landau, Lifshitz - Mechanics - Integration of the Equations of motion [closed]
I'm studying Landau, Lifshitz - Mechanics. Could someone help me with this problem ? =)
Problem 2 (Page 27 3rd Edition) Determine the period of oscillation, as a function of the energy, when a ...
0
votes
0answers
82 views
Elastic strings [closed]
Two elastic strings, $A$ and $B$, stretch by $30 \text{mm}$ and $60 \text{mm}$ respectively when a weight of $4 \text{N}$ is attached to each in turn. the strings are hung vertically from the same ...
1
vote
0answers
259 views
Lagrangian of pendulum with pivot point rotating about a circle [closed]
I just would like to know If I am on the right track with this stuff. I have scanned the work I have done, sorry if it is a little messy. Disregard the top most $\ddot x$
A disk of radius ...
2
votes
1answer
235 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
233 views
How to find angular velocity of a point inner a circumference
Let's consider a cicumference that have the center in the origin of axes and rotates around x-axes. Let's stick a bar in a point $A$ of this circumference and at the end of the bar let's stick a mass ...
3
votes
1answer
279 views
Writing equation for amplitude of driven harmonic oscillator in Lorentzian form
This harmonic oscillator is driven and damped, with the form:
$$\ddot{x} + \lambda \dot{x} + \omega_0^2 x = A \cos(\omega_d t)$$
Now, I have used the ansatz (guess): $x(t) = B \cos(\omega_d t + ...
1
vote
1answer
556 views
Rolling bowling ball with slipping
If a bowling ball is moving with some initial velocity while slipping, how far will it move before it begins to roll once it experiences static friction?
$\ddot{x} = \mu_{kf}g$
And there is also a ...
1
vote
1answer
321 views
Poisson brackets and angular momentum
I'm trying to find $[M_i, M_j]$ Poisson brackets.
$$\{M_i, M_j\}=\sum_l \left(\frac{\partial M_i}{\partial q_l}\frac{\partial M_j}{\partial p_l}-\frac{\partial M_i}{\partial p_l}\frac{\partial ...
0
votes
0answers
72 views
How does an oscillating particle in a non-inertial reference frame appear?
The general question is : given an oscillating particle in a non-inertial reference frame:
How would it appear from outside the non-inertial reference frame ?
How would an observer inside that ...
0
votes
0answers
38 views
Velocity of a sled and the angle of its sail [closed]
I have this mechanics problem, and, through I got an answer, I'm not sure at all it is the right one:
Imagine a sled with a single sail, which behaves like a solid body and is restricted to move ...
4
votes
2answers
391 views
Uniform chain falls off table Diff EQ
I really need some assistance setting up this problem. any assistance would be a Godsend:
a uniform heavy chain of length a initially has length ...
2
votes
1answer
203 views
Euler-Lagrange Equation
A particle moving towards the origin has initial conditions $x(t=0) = 1$ and $\dot{x}(t=0)=0$
If the Lagrangian is L:=$\frac{m}{2}\dot{x}^2 -\frac{m}{2}ln|x|$
This should satisfy Euler Lagrange ...
0
votes
2answers
53 views
How to show that if two masses($m_1$ and $m_2$) are connected($r_1<r_2$) with a string moving around a point A, they move with same angular velocity?
How to show that if two masses($m_1$ and $m_2$) are connected($r_1<r_2$) with a string moving around a point A( circular motion), they move with same angular velocity? In this special case if ...
1
vote
1answer
83 views
Spring coupled platforms & conservation of momentum - can it be solved with freshman physics?
This question came up as an exercise in a first year undergraduate course I was a TA for. It turned out to be a lot more difficult (impossible?) than anticipated...
Two platforms of mass $M_1$ and ...
0
votes
0answers
336 views
How to find the tension? [closed]
How do I find the tension in the string? And how should I find out if the boxes have moved?
0
votes
1answer
207 views
Ball rolling down an inclined plane going in to a loop
I apologize if this question is not up to par.
When I was doing exercises in basic mechanics I checked the answers and I can't seem to find what I'm doing wrong.
Suppose we have a ball with mass $m$ ...
3
votes
2answers
773 views
Normal Forces and Ferris Wheels
At the moment, I am reading an example problem regarding what was alluded to in the title. In this example problem, they say, "Based on experiences you may have had on a ferris wheel or driving over ...
1
vote
2answers
260 views
To find whether a particle is in equilibrium or not
Actually the following question came in an exam i gave yesterday. I know the site does not allow home-work type questions, but as I am having a conceptual problem in solving the question, I am posting ...
0
votes
0answers
174 views
Classical Mechanics: A particle move in one dimension under the influence of two springs [closed]
A particle of mass $m$ can move in one dimension under the influence of two springs connected to fixed points a distance $a$ apart (see figure). The springs obey Hooke’s law and have zero unstretched ...
0
votes
1answer
366 views
Determine the maximum height a pump can suck up water
I am working on a homework problem that presents the scenario of trying to raise water from a small reservoir of depth 8 m whose surface is 25 m below a pump that can maintain a pressure differential ...
1
vote
1answer
140 views
Clarification on a Goldstein formula steps (classical mechanics)
At page 20 of Classical Mechanics' Goldstein (Third edition), there are these two steps given between eqs. (1.51) and (1.52):
$$\sum_i m_i \ddot {\bf r}_i \cdot \frac{\partial {\bf r_i}}{ \partial ...
3
votes
1answer
173 views
Can I find a potential function in the usual way if the central field contains $t$ in its magnitude?
I'm working on a classical mechanics problem in which the problem states that a particle of mass $m$ moves in a central field of attractive force of magnitude:
$$F(r, t) = \frac{k}{r^2}e^{-at}$$
...
0
votes
0answers
38 views
Could you help and check my four easy dynamics tasks? [closed]
So I have four tasks to do and I have a guess for some of them but would greatly appreciate if you could help me be sure of it or clarify what I don't understand.
A car covers 2000m in 2 minutes and ...
