2nd law Definition and 292 Threads

Homework Statement An 8.5 gram slug is fired East from a 0.357 magnum hand gun held 1.5 meters above the ground. The muzzle velocity (as the projectile leaves the gun) is 1400 ft/sec. The bullet is accelerated at a constant rate as it travels through the 10 cm long barrel. After leaving the...

Homework Statement A rope of mass M and length ##l## lies on a frictionless table, with a short portion ##l_0##, hanging through a hole. Initially the rope is at rest. Find the length of the rope through the hole as a function of time. Homework EquationsThe Attempt at a Solution So I know...

Homework Statement A 0.25 kg particle moves in an xy plane according to x(t) = -15 + 2t - 4t3 and y(t) = 25 + 7t - 9t2, with x and y in meters and t in seconds. Find formulas at time t<35 sec for the (a) the magnitude and (b) the angle (relative to the positive direction of the x axis) of the...

I'm reading Thermodynamics: Foundations and Applications by Gyftoploulos and Beretta, because the authors claim to give a presentation of classical thermodynamics without "... the lack of logical consistency and completeness in the many presentations of the foundations of thermodynamics" [from...

Hi, rank newbie here, with my first post. This one is something I figure every first year student comes up with at some point, but I don't know enough keywords to Search for an answer. (I'm not a student except in the category "of life": this isn't assigned homework) I figger, using a bit of...

Homework Statement A sleigh with a mass of 150 kg from rest is horizontally towed to the left . This is done using a rope that makes an angle of 30 ° with the horizontale. The tensile force is 200 N. (Neglect friction forces.) a. What is the horizontal component of the force? b. What...

Homework Statement A skier glides down a slope, and has at the bottom of the slope, at the beginning of a horizontal piece, a velocity of 30 m / s. He begins to brake and after 4 seconds later has a speed of 10 m / s. The friction between the skis and the snow is 400 N during braking. a. What...

All of my information comes from my current chemistry class, I just want to know where I either may have misread, misinterpreted, or was mistold information. With the 2nd Law of Thermodynamics we can say $$[1]\space\space \Delta{S}_{universe} = \Delta{S}_{surroundings} + \Delta{S}_{system} >...

I have heard (read) much debate over the fundamental problems with white holes, mainly that they violate Thermodynamics by increasing entropy. However, I have also read that a black hole bends space-time enough to "connect" somewhere else as an Einstein-Rosen Bridge. So if the exact same event...

I am aware of the Second Law of Theromodynamics and I understand it to a certain extent, although still I am burdened with the frustration of being ignorant to why such a law exists. Please assist me.

can a resultant external force on a body change its mass but keep velocity of its centre of mass constant ? Is it practically possible - ##\vec{F}_{ext}=\vec{v}_{com}\frac{\mathrm{d} M}{\mathrm{d} t}## where F is nonzero

Homework Statement Here is the problem: An inventor claims to have developed a heat pump that provides a 180 kW heating effect for a 293 K household while only consuming 70 kW of power and using a heat source at 273 K. Can this claim be possible? Homework Equations COP of heat pump = Qh/W COP...

I have a quick question concerning the 2nd law of thermodynamics. So my textbook uses an illustration to explain how the violation of the Clausius statement of the 2nd law implies a violation of the Kelvin-Plank. But while looking over the diagram I stated thinking about a certain situation. In...

Homework Statement A ball whirling on the end of a string, length L Maximum tension in string before it breaks: T sub break Find an equation for the maximum speed of the ball , V sub max, in terms of the ball's mass, M, the breaking tension T sub break, and the gravitational acceleration g...

Entropy has units of kJ/kg K and energy has units of kJ. So my question is if entropy is not conserved how is energy conserved when there is a unit of energy within entropy?

I think I have never seen a force equation for massless particles, I wonder if such thing exist or if not why not?

I'm a newbie (obviously), but I just read this recent paper describing an "experimental realization of an autonomous Maxwell’s demon" (along with this review). I think I understand the general concept of Maxwell's thought experiment well enough (from a layman's perspective), but I'm having...

Say I have an infinite cylinder filled with monoatomic gas and on one end has a piston attached to it. I now supply heat to the cylinder. The gas expands thereby converting all of heat energy into physical work(displacement of the piston). Since the cylinder is very long it eliminates the...

Homework Statement http://postimg.org/image/z9uzlyt3p/ Homework Equations F=MA W=MG The Attempt at a Solution the force on the block must be gravity *its mass (weight) since it hangs, but because of the pulley and other box pulling the other way, creating an T, the force on the hanging block...

Hi guys, I'm an arts undergrad student with very little knowledge of the sort of physics I'm about to ask. I was wondering if there is a calculation to work out the differentiation between running at a particular speed say 10mph against wind coming towards you at 15mph. As well as it being on...

I am trying to explain why a small object falling from a short distance on another object does not have the same impact as a bigger object falling from the same height on another object by using Newton's 2nd Law but I get stuck all the time. Can somebody please help me?

The question is basically, a block with a mass "m" is sliding up and down on a incline plane with an angle of inclination that is β. The leaving velocity (Start velocity v_i) is v0 and the frictionskoefficient is between the plane and the block is μ. Determine the velocity "v" when the block...

Homework Statement For part (iv) 2 and 3 of this question, I don't understand why for 2) terminal p.d. of A is the e.m.f of A minus the p.d. across the internal resistance of A i.e. Va = 4.4-(0.24x2.3), I=0.24A But for 3) the terminal p.d. is the e.m.f of B PLUS the p.d. across the internal...

I recently posted about a browser-based educational app that graphs the position, velocity, and acceleration of the mouse's vertical motion. In the same spirit, I've written an app that demonstrates the statistical basis of the second law of thermodynamics by simulating the free expansion of a...

Homework Statement An ideal gas expands isothermally in contact with a heat source. ∆U is zero in this case because it is an ideal gas and T=constant. Is this against Kelvin-Planck statement? Homework Equations pv=nRT dW=-pdV Kelvin-Planck statement: There is no process whose only result is...

If a constant force is applied to an object and the force is pushing the object up a inclined ramp with constant velocity what is the acceleration if mass is unknown? F=ma F=m (1m/s^2) If i apply this equation then acceleration is 1m/s^2. Am i applying this formula correctly? thanks

Homework Statement Show that Newton's Second Law is NOT valid in a reference frame moving past the laboratory frame of problem 1 with a constant acceleration? Problem 1: In a laboratory frame of reference, an observer notes that Newton's Second Law is valid. Show that it is also valid for an...

Homework Statement Show that Newton's Second Law is NOT valid in a reference frame moving past the laboratory frame of problem 1 with a constant acceleration? Problem 1: In a laboratory frame of reference, an observer notes that Newton's Second Law is valid. Show that it is also valid for an...

Homework Statement Kepler’s 2nd law of planetary motion says that the radius vector drawn from the Sun to any planet sweeps out equal areas in equal time intervals. By considering the small area swept out by the radius vector in time dt, show that \frac{dA}{dt} = \frac{L}{2m} , where L is...

I saw an explanation for why Jupiter has a slower tangential velocity in its orbit compared to inner planets and it stated: "Remember that by Kepler’s second law, the planets each sweep-out the same area in the same amount of time. The outer planets’ elliptical orbits are considerably larger...

Chestermiller submitted a new PF Insights post Understanding Entropy and the 2nd Law of Thermodynamics Continue reading the Original PF Insights Post.

Homework Statement Show that ##\Sigma \vec F = \frac {d \vec p}{dt} ## Homework Equations ##\Sigma \vec F = m \vec a ## ## \vec a = \frac {d \vec v}{dt} ## ## \vec p = m \vec v ## The Attempt at a Solution We need to prove that ## \frac {d \vec p}{dt} = m \vec a ##. When I physicists...

While reading some articles on Wikipedia I came upon one interesting statement that essential says (I've rephrased for clarity; correct me if I'm wrong): "The Time-asymmetry of the second law of thermodynamics is due to the initial conditions of our universe" Can someone elaborate on what...

The problem states that a 3.4 kg object hangs at one end of a rope that is attached to a support on a car. The car and cruisin' and is accelerating, when it does this, the rope makes an angle of 23 degrees with the vertical. Acceleration of gravity is 9.8 m/s/s and the question is asking for the...

Homework Statement How do i compute theoretical acceleration and experimental acceleration? The Attempt at a Solution For the first sets of data, the experimental equation, i first averaged the timings. Then i used: s = ut + 0.5at^2, where u=0 0.7 = 0.5*a(2.11seconds)^2 a...

I was reading Cengel's thermodynamics and noticed that he uses a thought experiment to show that there is no machine that is more efficient than the Carnot reversible machine. He says that both a reversible machine and an irreversible machine are connected to high and low temperature deposits...

I have read quite a few discussions about this topic of entropy and if this universe has a truly closed or, as I prefer to describe it "undisturbed", system and I have read some discussions about a freezer and chilling ice cubes etc. etc... To my extent of reading these conversations no one has...

Hello, I have a problem to do with a chain. You have a table with infinite drop and a chain of length l. The chain is let off at the end of the table. Assuming a frictionless table, calculate an expression for the speed of the chain. Could anyone help with this please? Best wishes...

Homework Statement I am given the following dynamic system. I want to find the transfer function, θ1(s)/T(s). The main body of the satellite, J1, acts like a large mass flying through space; space is essentially without friction and therefore no damping is imparted on the main body...

Sorry, but this will be a long post. This isn't homework, I'm reviewing physics after many years of neglect. Halliday & Resnick, 4th Ed., section on variable mass and rockets, refers the interested reader to an article, "Force, Momentum Change, and Motion," Martin S. Tiersten, Am. J...

Homework Statement Attached Homework Equations Attached The Attempt at a Solution 2ac + 3 = 0 => ac = 1.5m/s^2 upwards For FBD of C, Newton's 2nd law 2T - 200g = 200*1.5 => T = 1131N For FBD of the beam, Take moments about A, and assume beam is rigid (CCW positive): 2.5T - 3T -...

Homework Statement Apply Kirchhoff's laws to find the current at point X in the circuit shown. What is the direction of the current? Homework Equations V = IR Kirchhoff's 1st law: ∑Currents entering junction = ∑Currents leaving junctions Kirchhoff's 2nd law: ∑EMFs in a loop =...

I can't derive it properly even though it should be easy: From Newtons 2nd law: m dv/dt = -eE => v(t) = -meEt + v(0) (the latter will average out when taking average) Now the Drude assumption: An electron will on average travel a time τ before being scattered and starting its motion...

Homework Statement Starting from a rest position, how long will it take a 50 kg cyclist riding a 10 kg bike to reach a speed of 4 m/s if the resultant force acting on the bicycle is 48 N? Homework Equations F=ma Vf=Vi + at The Attempt at a Solution F=ma (F-48)=(50+10)(a)...

What are some open problems in the interplay between Quantum Mechanics and the 2nd Law of Thermodynamics? thanks

F = d(mv)/dt Newtons 2nd Law F = -kx Spring Force F = -cv Damping Force d(mv)/dt = -kx + -cv How would you correct the equation for a damped harmonic oscillator for relativity. If it is possible. I just want a one dimensional solution unless you have to go...

I’m supposed to prove that if ΣF(v) = -Av^2, where A is a constant, then Δx = m/A * ln (v0/v) by using Newton’s second law in the form ΣF = m dv/dt. I can solve the problem by using the form ΣF = mv dv/dx; however, it’s specifically stated that I’m not allowed to use the law in that form...

Not everyone likes the idea of Universe ​​created from a point singularity, so recently grows in popularity the cyclic model - that our Universe will finally collapse and use obtained momentum to bounce (so-called Big Bounce) and become the new Big Bang. One might criticize that we "know" that...

I'm having trouble finding any sources that discuss equations of motion that take into account a changing moment of inertia. Just looking at the scaler case, angular momentum is L = I\omega Then, according to the 2nd law, \tau = \frac{d}{dt}(L) = \dot{I}\omega + I\alpha Is this correct...

The book that I use (Concepts in Thermal Physics by S. and K. Blundell) states the second law in two ways. The way they state the Kelvin version is "no process is possible whose sole result is the complete conversion of heat into work." How does that fit in with the isothermal expansion of an...