All Questions
19 questions
0
votes
1
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92
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Why isn't work $Fd \sec \theta$? [closed]
In the following image if force the triangle PAN was right angle at P then the component of force in the direction of displacement would be $F\sec\theta$ so work $F*Displacement(AC)*\sec \theta $.
I ...
4
votes
0
answers
166
views
Why is the ratio of components of kinetic energy equal to the ratio of kinetic energy to total energy for a projectile whose range is maximized?
The launch angle $\theta$ that maximizes the range of a projectile in a uniform gravitational field is
\begin{align}
\theta = \arctan\left(\frac{v_o}{\sqrt{v_o^2 + 2gh}}\right), \tag{1}
\end{align}
...
- 41
30
votes
4
answers
73k
views
Difference between momentum and kinetic energy
From a mathematical point of view it seems to be clear what's the difference between momentum and $mv$ and kinetic energy $\frac{1}{2} m v^2$. Now my problem is the following: Suppose you want to ...
- 2,740
1
vote
0
answers
44
views
Violation of conservation of energy [duplicate]
Sand runs from a hopper at a constant rate $\frac{dm}{dt}$ onto a horizontal conveyer belt driven at a constant speed $v$ by a motor. The power needed to drive the belt can be calculated as follows:
...
- 378
0
votes
0
answers
45
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If we know the location of object at different times, what more can we find out from it?
I'm brushing up on my physics, and I've been struggling with this problem in my head. I hope you can help.
Let's assume that we have some object/particle that only moves along a single axis ($x$). We ...
- 3,778
-2
votes
2
answers
46
views
Equation for Work required to achieve a certain velocity [closed]
If we are trying to find the work required to get an object moving at velocity $v$, and we start with $w = f\cdot d$, we can then make the following substitutions:
substitute $f$ with ma: $w = m\cdot ...
- 5,496
1
vote
0
answers
136
views
Difference between eigenvalues of the potential energy Hessian vs. "generalized" eigenvalues with respect to a kinetic energy "metric"
Simple version
Consider if we have a Lagrangian defined by
$$L(q,\dot{q}) = \frac{1}{2} g_{ij}(q) \dot{q}^i \dot{q}^j - U(q) \tag{1a}$$
where the potential energy $U(q)$ has a single minimum at $q=0$ (...
- 3,780
0
votes
2
answers
112
views
How is energy conserved in terms of "Work"
Basic equation of work is given by $F\cdot s$. When work is done, the energy is stored either in form of potential or kinetic. My question arises when we look at a case of applying $m g$ of force ...
- 77.9k
4
votes
1
answer
186
views
Why is the kinetic energy a fixpoint of the Legendre transformation?
Question: Why is (from an intuitive standpoint) the kinetic energy $T$ a fixpoint of the Legendre transformation, i.e. $\frac{\partial T}{\partial \dot q}\dot q-T = T$ for any general coordinate $q$? ...
- 4,113
7
votes
2
answers
2k
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What is the highest energy position for a double pendulum? And for which energy positions is it chaotic?
Math/physics teachers love to break out the double pendulum as an example of chaotic motion that is very sensitive to initial conditions. I have some questions about specific properties:
For a ...
- 103
1
vote
2
answers
414
views
Inconsistent Results with Momentum and Kinetic Energy
A speed skater with a mass of $m_1$ kg is moving at $v_{1i}$ m/s. He prepares to push the next speed skater of mass $m_2$ kg moving at $v_{2i}$ m/s. After the push, the velocity of the first skater ...
- 58.6k
1
vote
1
answer
213
views
Kinetic energy is different in different frames of reference? [duplicate]
If velocity is a relative term then a body would possess different Kinetic Energy in different frames of reference.
How can a body have different energies simultaneously for different observers ?
- 1,856
1
vote
1
answer
7k
views
Calculating velocity of a car based on engine power
Is it possible to calculate the velocity of a car accelerating from rest at full capacity given the power of the engine and the mass of the car? I have a method of solving the velocity with respect to ...
2
votes
3
answers
528
views
What was the motivation behind the work formula?
Surely there must be a reason we decided to use this as a metric for mechanical energy.How was it developed and what made it more acceptable than other work formula candidates (Like force over time, ...
- 1,823
3
votes
3
answers
881
views
Is there an intuitive explanation of the work formula?
Upon learning calculus, I decided it was time to derive all of classical mechanics to give myself a good understanding of physics. What I found was that, while trying to do so, I would need some ...
CommunityBot
- 1
0
votes
1
answer
126
views
Why do systems with a fixed gear-ratio still use gears?
From my understanding, there are two uses of a gearing system: to change the speed of output rotation (trading it with torque), and to change the axis of rotation. Now, in a car, for example, it is ...
- 10.8k
0
votes
2
answers
6k
views
Kinetic energy dissipation in braking a vehicle
Let's say a vehicle that weighs 20t is hauling along at 50m/s and we want to brake it down to a full stop.
The kinetic energy we need to dissipate into heating up the brakes is
...
- 42.3k
2
votes
2
answers
954
views
What is the percentage of energy recovery in Kinetic Energy Recovery Systems(KERS) in cars?
Kinetic Energy Recovery Systems (KERS) use flywheels to recover energy from the kinetic motion of cars. They use a rotating flywheel that generates energy as it rotates- this generates the electric ...
CommunityBot
- 1
0
votes
2
answers
212
views
Query into the cumulative velocity of mounted platforms
Consider throwing a stone at an object from rest, it travels at Vms-1. Now throw that stone whilst running at Ums-1. It seems in the latter scenario the total speed of stone is V + U. Now imagine ...
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