1
vote
1answer
34 views

What factors indicates inelastic collision?

I am watching this example from Wikipedia: I am wondering what factors would indicate that the collision of 2 objects will be inelastic (I know macroscopic scale impacts are never perfectly ...
0
votes
1answer
35 views

Why is the change in height for mass be $2h$ in this question? [closed]

Could anyone tell me why the height is $2h$?, and is the total gpe in a system where the masses are balanced 0?
0
votes
2answers
55 views

Who of these cyclist travel takes less time? [closed]

There are two cyclist. They start off with equal velocity $v_0$. The first one bikes a straight path, while the other bikes through a valley, something like this: We assume friction doesn't affect ...
3
votes
2answers
81 views

Optimal speed for the water wheel

The hydroelectricity plants extract the potential energy of highly deployed massive object (water) as it falls down. Without turbine, all that energy would be converted into speed (kinetic energy) at ...
2
votes
0answers
27 views

Double pendulum find first integral [closed]

Consider the following situation of a double pendulum in 2D. We found the moving equations as $$ \ddot{\theta_1}=-L_1\sin\theta_1 + \frac{m_2}{m_1}\cos\theta_2\sin(\theta_2-\theta_1),\\ ...
3
votes
3answers
93 views

How is angular momentum conserved if a bullet hits a wheel?

Suppose my system involves: 1) A mounted wheel with some outward flap 2) A bullet already in motion Initially the net angular momentum is 0 and the net kinetic energy is just that of the speeding ...
0
votes
1answer
35 views

Doing a spring experiment, and need to find the stretch required

I'm doing an experiment where I have to calculate the stretch of a spring needed for it to launch itself into a trashcan located some distance away. The spring is located on the edge of a ramp that is ...
0
votes
3answers
91 views

Why isn't angle of launch used in this kinetic energy equation?

Question: A stick is thrown from a cliff 27 m high with an initial velocity of 18 m/s at an angle of 37 degrees above the horizontal. a) use the law of conservation of energy to determine the speed ...
-2
votes
2answers
52 views

Difference between two equations

So again I have two equations: $$K= \frac{1}{2} m v^2 + \frac{1}{2} I \omega^2$$ And $$K_w = \frac{1}{2} I \omega^2 $$ What's the difference between these two? Thanks.
0
votes
2answers
226 views

Loop-the-loop question [closed]

Problem: The marble rolls down the track and around a loop-the-loop of radius R. The marble has mass $m$ and radius $r$. What minimum height $h$ must the track have for the marble to make it around ...
2
votes
2answers
109 views

Potential and kinetic energy on spherical surface

A small particle of mass $m$ is atop of a semi-sphere as shown in the figure. A little push was given to the particle. Prove that the particle will leave the spherical surface at a height of ...
4
votes
4answers
130 views

Does car have more kinetic energy when turning?

I asked this Phys.SE question Does car lose kinetic energy when turning? Assume a car turning without losing its speed by holding to a point by a rope. IMO, while the car is turning, its kinetic ...
0
votes
1answer
103 views

Loss of kinetic energy in inelastic collision [duplicate]

I know that momentum and energy are always conserved in collisions, but if we have a perfectly inelastic collision in which an object sticks to another object $m_1 v_1 + m_2 v_2 = (m_1+m_2)v_{12}$, ...
0
votes
1answer
61 views

Integrating for speed [closed]

Trying to determine the speed of a falling body with respect to traveled distance and initial speed. I've been provided with the following equation for acceleration as a function of distance and the ...
0
votes
0answers
75 views

More on the closed-form for a simple pendulum

I've learnt about the simple pendulum, and while the regular curriculum only uses the linear approximation of $\sin\theta$ to obtain $\ddot\theta+\omega_0^{2}\theta=0$. I tried to find out about a ...
1
vote
1answer
60 views

Conservation of energy quick question

Say we had a particle moving in a frictionless funnel and was projected horizontally. If we had some initial conditions for the energy E, then would these conditions be the same always? For ...
0
votes
1answer
129 views

Atwood machine with spring

I'm just beginning to learn about Lagrangian mechanics, and I am asked to find the kinetic energy of this Atwood machine (See figure). I am told, that the kinetic energy should be: ...
1
vote
2answers
67 views

Using an electric winch to compress a spring and launch an object

I'm having trouble grokking the relationship between a winch's pull/torque and a spring's potential energy. I would like to compress a spring using an electric winch and figure out how far it will be ...
0
votes
2answers
243 views

Rolling disk in inclined plane and flat plane? [duplicate]

A disk is rolling (not sliding) in the inclined plane with initial velocity of zero. So there is friction between disk and plane. But when we use the energy conservation rule, we consider as: ...
0
votes
1answer
155 views

Confusion over the gravitational potential energy inside a sphere

I'm confused over the concept of gravitational potential energy inside a sphere. I understand that the gravitational potential energy inside the sphere is supposed to be a constant $U = ...
0
votes
2answers
82 views

Angle rotated by a rod when it's hit by a pendulum

Consider a pendulum of length $h$ with a bob of mass $m$ it is held horizontally at and angle of $90^{\circ}$ with the vertical. A rod of mass $M$ and length $h$ is pivoted at its upper end and this ...
0
votes
2answers
53 views

Distribution of Kinetic energy after an Impact

How does the huge amount of kinetic energy of some fast object like a meteor or rocket etc. gets distributed into various kinds of energy like kinetic, sound, light etc after making an impact with ...
3
votes
2answers
107 views

Maximum permissible speed while going down a ramp

So, I was playing hill climb racing and I noticed that if we move with high speeds towards a ramp going down we just jump it off. While lower speeds, help us to stay in contact with the ramp. ...
1
vote
2answers
89 views

Energy of a damped oscillator

$$ E=\frac{1}{2}m\left(\frac{dx}{dt}\right)^2+\frac{1}{2}m\omega_0^2x^2. $$ This is the equation for the energy of a oscillator. The second term is the potential energy. Now, my question is, will ...
2
votes
2answers
196 views

What will be the velocity of a comet is falling to the Earth from infinity at the time of impact if Earth had no atmosphere?

What will be the velocity of a comet is falling to the Earth from infinity at the time of impact if Earth had no atmosphere? the comet is falling radially towards the earth. Will this velocity be ...
0
votes
1answer
90 views

Where does the potential energy go when mass is lifted out of Earth's gravitational field?

There is a finite amount of energy needed to be spent on a rocket or a rock that is taken out of the Earth's gravitational field. Lets suppose the rock is taken far enough to have no effect of Earth's ...
0
votes
0answers
41 views

Determining impact velocity over long distances [duplicate]

Everything I have found concerning impact velocity from a given height deals with constant acceleration due to gravity. I would like to know how to work in varying acceleration into the equation. So, ...
1
vote
0answers
33 views

Mechanistic description of leverage

How would you describe how a lever is able to apply a large for to an object from only a small applied force without recourse to conservation of energy? Is there a purely F=ma type derivation? For ...
0
votes
4answers
186 views

Does car lose kinetic energy when turning?

I am writing simple car simulation. Assume non friction, then in straight line the car doesn't lose speed. But what if the car is turning, there should be some kinetic energy loses to change the ...
0
votes
2answers
192 views

Energy transfer in elastic collision [duplicate]

In a given reference frame where object 1 (with known mass and velocity) collides elastically with object 2 (with known mass and velocity), can we identify which object loses kinetic energy? Is it ...
4
votes
2answers
3k views

Perfectly centered break of a perfectly aligned pool ball rack

Imagine the beginning of a game of pool, you have 16 balls, 15 of them in a triangle <| and 1 of them being the cue ball off to the left of that triangle. Imagine that the rack (the 15 balls in a ...
-2
votes
2answers
293 views

How energy conservation is not violated here?

If I lift a book of mass $m$ from the ground and put it at height $h$,then initial and final energies with respect to ground are 0 and $mgh$ respectively. So how energy is conserved here?
0
votes
1answer
106 views

A variable mass system (cart of sand with a hole)

Imagine we have a frictionless semicircular skateboard ramp and we release a cart filled with sand from one edge of the ramp. The cart has a hole and it loses sand at a constant rate. My question is ...
0
votes
0answers
44 views

absorbing energy from explosion

The other day in physics, we went to visit a workgroup that was developing a wall that would absorb energy from explosions (it was a joint project with the military academy). The first prototype they ...
1
vote
2answers
117 views

Rigid bodies - the wheel

As I've been taught lately in my mechanics course: the wheel has a unique property: at every moment of motion, the touching point between the wheel and the ground is not in movement and ...
1
vote
3answers
483 views

When is energy conserved in a collision and not momentum?

Consider the following example: A bullet of mass 45g is fired at a speed of 220 m/s into a 5.0 kg sandbag hanging from a string from the ceiling. The sandbag absorbs the bullet and begins to ...
1
vote
4answers
147 views

Solids: is energy expended in some fashion by, say, a table to keep the top from sinking down against gravity?

A friend and I were discussing this, and couldn't decide. Since it takes energy to physically raise something up above the planet's surface, does it continue to require energy in order to keep it ...
1
vote
0answers
61 views

Collision Between Two Particles: Writing the Mass As A Function of The Angle [duplicate]

Suppose we have two masses, $m_1$ and $m_2$, where $m_2$ is at rest, and $m_1$ is headed directly towards $m_2$. I would like to write the ratio of the masses as a function of the angle. Using ...
13
votes
2answers
433 views

Conservation of Mathematical Constraints when deriving Energy and Momentum from $F=ma$

Background: Starting from $F = ma$, integrating with respect to time, and using basic calc, one can derive $\int Fdt = m (v_f - v_i)$ Starting from $F = ma$, integrating with respect to distance, ...
1
vote
1answer
87 views

How would you quantify and predict the internal friction and efficiency of a bungee cord?

I am in an introductory physics class and we have been working with Gravitational Potential Energy, Elastic Potential Energy, Kinetic Energy and the Law of Conservation of Energy in relation to bungee ...
24
votes
6answers
2k views

Why are rockets so big?

I'm curious why rockets are so big in their size. Since both the gravitational potential one need to overcome in order to put thing into orbit, and the chemical energy burned from the fuel, are ...
2
votes
0answers
100 views

Conservation of Mechanical Energy [closed]

I am currently trying to tackle the problem: A 2.0 kg bundle starts up a 30° incline with 125 J of kinetic energy. How far will it slide up the plane if the coefficient of friction is 0.30? ...
5
votes
3answers
201 views

Does unitarity imply conservation of energy?

Not too long ago, someone began to discuss the thinking and motivation behind the Lagrangian and its formalism for the Newtonian framework and an intuitive understanding of such formalism. Somehow, it ...
2
votes
3answers
721 views

Gravitational Potential Energy (GPE) to Kinetic Energy (KE) transfer in Satellite Orbits

I am stumped by a mundane A Level Physics question (teacher of physics here obviously a bit short of practice!). My colleagues and I are stumped and were wondering if any one could help us. It ...
2
votes
1answer
308 views

How to understand Feynman's reasoning about perpetual motion?

I'm studying Feynman's Lectures on Physics, and I'm not really understanding his reasoning here: Consider weight-lifting machines $\overline{}$ machines which have the property that they lift one ...
1
vote
1answer
676 views

Are principle of Conservation of energy and principle of conservation of momentum consequences of Newton's laws?

It is known that principle of Conservation of momentum and principle of conservation of energy are two fundamental principles of physics.But in RP Feynman's Lectures of physics, in the chapter of ...
0
votes
1answer
709 views

Gentle slope vs steep slope

Take for example a slide of 3m tall. Would an object (starting from rest) sliding down a gentle slope have a lower speed than a steep slope? (Note: Height of slide is the same,disregard friction.) ...
-1
votes
1answer
274 views

Speed of a falling pencil [closed]

If you balance a pencil of length $d$ on its tip, and let it fall, how do you compute the final velocity of its other end just before it touches the ground? (Assume the pencil is a uniform one ...
2
votes
1answer
372 views

Dominos vs. Conservation of Energy

In this video a single flick of a finger tips 116000 dominos. Domino video I understand the work that needs to be done to move 116000 pieces (at least 100 kilos) of plastic is greater then that ...
1
vote
3answers
752 views

SMBC ball bouncing problem

This comes from a Saturday Morning Breakfast Cereal (SMBC) comic with a joke answer. The problem states: A 5 kilogram ball is shot directly right at 20 meters per second from a height of 10 ...