2nd law Definition and 292 Threads

Homework Statement A 500kg crate is pushed with a 2000N force. The force of the sliding friction acting on the crate is 1900N. How fast will the crate be moving after 10 seconds? How far will it have moved in this time? Determine the net force Homework Equations a = \SigmaF/m...

Homework Statement A 10,000 kg rocket is acted upon by a upward thrust of 118,000N How fast will the rocket be moving after 20 seconds? How far will it have moved in this time? Also, how do i determine the net force Homework Equations a = \SigmaF/m d=1/2at2+vit The Attempt at a Solution...

Homework Statement So I am coming up with a word problem dealing with N2L. It goes like this. I have an object on top of a cliff i want to get, so i attach a pulley to the edge of the cliff. Now i tie my self to the object and string it with the pulley. To get the object down I will rappel off...

Homework Statement Homework Equations Newton's 2nd Law F = ma Torque Equation τ = Iα The Attempt at a Solution Well I know I have to write separate equations for the masses and tensions so I got this: T1 - m1g = m1a T2 - m2g = -m2a -----> (negative because acceleration...

Homework Statement While walking down the hallway, a student drags his 4kg school bag. The force on the bag is 20N [60 degrees above the horizontal]. If the bag moves at a constant speed, what is the coefficient of friction? Homework Equations Fn = Fg-Fasintheta Ff = u(Fn). The...

A 15,000 kg rocket blasts off from Earth with a uniform upward acceleration of 2.0 m/s2 and feels no air resistance. The thrust force its engines must provide during this acceleration is 30,000 N upward. Apparently this is FALSE! I don't understand why F=MA 30000N=15000kg*2m/s^2...

Homework Statement A proud homeowner is out mowing their lawn. If the force of friction on the mower is 50.0 N and it is accelerating forward at 0.15 m/s2, what is the magnitude of the applied force if the owner is pushing on the handle of the mower at an angle of 70 below the horizontal...

Homework Statement An arrow, starting from rest, leaves the bow with a speed of 25 m/s. If the average force exerted on the arrow would be doubled, all else remains the same, with what speed would the arrow leave the bow? Homework Equations force = mass x acceleration The Attempt at a...

Homework Statement http://gyazo.com/f075da031d0e9d66f269e27628619082.png http://gyazo.com/525919e03d92ae9efad90cc06995ec1b.png Homework Equations F = ma F = 0 The Attempt at a Solution T = Fg for M1 M2 = T - ma = T-M2a I don't know what to do after this.

Hello, For a reversible heat engine between temperatures T_1 and T_2, the ratio of heat going in and out the engine is \frac{Q_1}{Q_2} = \frac{T_1}{T_2} (second law). Say T_1 = 200 K and T_2 = 273 K, then heat goes from 2 to 1 and as we can see, the ratio of heat that goes in the engine is...

Homework Statement A heat pump has a coefficient of performance of 3.70 and operates with a power consumption of 6.91 103 W. (a) How much energy does it deliver into a home during 1 h of continuous operation? 9.2x10^7 J (b) How much energy does it extract from the outside air? ? JHomework...

Rectennas are diodes attached to antennas. With current technology they can convert EM waves with frequency up to \approx 1 THz to electricity. Imagine an isolated room at 300^{o} K containing a black object and a rectenna. By Planck law, the black object radiates about 450W/m^{2}, of which...

General entrpy question from a book- (not a homework quesiton): When a room temp object is placed in a refrigerator, heat flows out of object and its entropy decreases. Indeed, the refrigerator may be said to be a device for sucking entopy out of warm objects. How can such a decrease in...

I understand that force is equal to the time derivative of momentum, or d(mv)/dt. Then what happens if the velocity is constant and only the mass is changing. Does this mean there will be a force. If so, in what direction since I am assuming it is still a vector. Also, what if the mass and...

Imagine a closed isolated system consisting of 2 rooms separated by a window. The window is built with one layer of material that has refractive index 1.5 and one layer of material that has refractive index 2, for a wide range of wavelenghts (say 1 \mu m - 50 \mu m), and low absorption. The side...

I recently attended this lecture by Physicist Daniel Sheehan, any opinions about the 2nd law soon violated in Laboratory Experiments? (and we are not talking about background fluctuations, etc). Experimental Challenges to the Second Law of Thermodynamics D.P. Sheehan, University of San...

This might be easy but apparently I haven't thought about long enough: Suppose a collection of particles with significant thermal energy are vibrating such that they emit electromagnetic radiation. Because of this, they cool down. Cooling means that their entropy decreases (classical...

Homework Statement A person weighs a fish of mass m on a spring scale atached to the ceiling of an elevator. (a) Show that if the elevator accelerates either up or down, the spring scale gives a reading different from the weight of the fish. Homework Equations \SigmaFy=T-Fg=may...

Homework Statement Block B rests upon a smoot surface. If the coefficients of static and kinetic friction between A and B are mu_s=0.4 and mu_k=0.3, respectively, determine the acceleration of each block if P=6lb. (picture attached below) Homework Equations Using Newton's Second Law...

F = dp/dt = d(mv)/dt = m(dv/dt) + v(dm/dt) = a + v(dm/dt) i don't understand why d(mv)/dt = m(dv/dt) + v(dm/dt) can somone help ? TNX !:smile:

1. Keeping the temperature constant, does the rate of emission from a black body depend solely on its surface area? 2. If it does, let's consider the following: we have two black bodies in our system, A and B lying close to each other. Both are at same temperature but the surface area of A is...

I am new here and have always loved the history of science as much as the science itself. I have been intrigued by the 2nd law of thermodynamics and entropy for a long time but have also had something about its evolution that bothered me. So I'll summarize its stated development from my...

[SOLVED] Motion (Newton's 2nd law + weight question) Homework Statement A waterskier of mass 70 kg is towed in a northerly direction by a speedboat with a mass of 350 kg. The frictional forces opposing the forward motion of the waterskier total 240 N. (a) If the waterskier has an...

The amount of black body radiation is proportional to the albedo. Microscopically, this is a result of the fact that the probability of process ‘wall absorbs a photon’ is equal to the probability of the reverse process: ‘wall emits a photon’ Lets assume that it is not true, and probability of...

Would the world fall apart and be destroyed if this law ceased to be constant? If not, how can we/do we speculate what would be different? Thanks!

Homework Statement A car weighing 15000N experiences a drag force of 1200N. The car travels 30m/s on a level highway. The coefficient of kinetic friction is 0.2. If the car travels for 10s at this speed, calculate the power the engine produces. The car then goes up a 10 degree constant...

Dear All Can't get my head around this. Entropy of the universe (system+surroundings) always increases. But why? G = H - TS G = Energy available for work H = Enthalpy of reaction How can the energy available be greater than the enthalpy of the reaction? There must be some input from...

hello forum, i am struggling with the conceptual understanding of this problem: Given two blocks, one on top of the other. There is friction between the two blocks. The upper block is pulled with a force F. Thanks to friction, as long as F is smaller or equal to the static friction...

Block inside a spinning cone -- Newton's 2nd Law problem Homework Statement See attempt at solution. I have attached everything there.Homework Equations F_net = m * a_n (net force) W = mg (weight) a_n = 4*pi^2 * R * f^2 ... formula for "normal" component of acceleration where R = radius, f =...

Homework Statement In this problem we explore a slightly more realistic model of a rocket's acceleration still neglecting air resistance. Consider a rocket fired straight up from rest burning fuel at the constant rate of b kg/s. Let v=v(t) be the velocity of the rocket at time t and suppose...

Homework Statement A 5.4 kg mass and a 6.2 kg mass are tied to a light string and hung over a frictionless pulley. What is the tension in the string? Homework Equations F=ma The Attempt at a Solution Not sure how to do this one. I know the tension on the string will be the same at both...

Homework Statement Show that the form of Newton's Second Law is invariant under: (a). a Galilean Transformation (GT) in 1-Dimension. (b). a Galilean Transformation (GT) in 2-Dimensions. (c). a Galilean Transformation (GT) in 3-Dimensions. Homework Equations Newton's Second Law...

Homework Statement A baseball of mass m is thrown vertically upward from a height r=0 with a speed of 20 meters/sec. The gravitational force on the baseball has a magnitude mg (m = mass, g=9.8 meters/sec2 is the acceleration due to gravity) and is directed downwards. Using Newton's second...

If we make a diff. equation from Newtons's 2nd law, and solve it, we will get x(t), where x(t) is the displacement as a function of time. what do the shape of the graph x(t) means? Does it give the trajectory of the motion?

Homework Statement A 1000 kg elevator is held up by two cables. If each able exerts a force of 6000N upwards upon the elevator, find the elevator's acceleration.Homework Equations Fg=mg FNET=maThe Attempt at a Solution I started with a force diagram to help me and then I think I'm supposed...

Can anyone give me the equation for the second law of thermodynamics... Please. Thanks

Hi all, here is a problem that has popped into my head every so often for the last year or so: A small, low-mass body is moving at a constant velocity of 1000m/s through a vaccuum, so it has no acceleration or deceleration i.e. a=0. Now let's say you are an astronaut and you are floating...

Homework Statement A load of 200kg is lifted through 50m by a vertical cable. The load accelerates uniformly from rest for 20 seconds, travels at constant speed for 10 seconds then decelerates to rest in a further 10 seconds. Find the maximum speed attained and the tension in the cable at each...

Consider a conical pendulum with a weight on it and that makes some angle with the vertical. I am told to find the radial acceleration of the weight and someone showed me how it is solved but I don't understand why: I am told to set Tsin@ = m(ar) *ar = radial acceleration ar = (Tsin@)/m...

So i have this general question. When the situation arises in which there are velocity and/or position depended forces acting on an object, would it be generally easier to use the work energy theorem or Newton's 2nd law & kinematics in predicting the motion? My guts tell me it will be work...

Well these two problems were from my quiz, and if I don't find out how to solve them soon, I'm going to spend my whole weekend thinking about them. D8 I'll try to remember the problems as best I can. 1) An astronaut is in space, in the midpoint of two stars that have the same mass. If all...

So is it true that if you have a constant velocity therefore you have no change in acceleration so A=0 and if you have no acceleration then you have no Fnet? And is that the case in ANY force problem? Thanks!

Mechanics:Dynamics (Newton's 2nd Law?) Homework Statement A sphere S with a mass of 5 kg is attached by a rigid rod to 1 kg block B which is free to slide with no friction in a horizontal slot. The system is released from rest. At the instant when it is released, find the tension in the...

Homework Statement A sphere S with a mass of 5 kg is attached by a rigid rod to 1 kg block B which is free to slide with no friction in a horizontal slot. The system is released from rest. At the instant when it is released, find the tension in the rod and the accelerations of both blocks...

Is it possible to deduce that a black hole must have something akin to Hawking radiation due to the 2nd Law of Thermodynamics? Let us consider for now a purely classical black hole. The event horizon is effectively a 'light diode' in that if light can pass through in a particular direction...

I'm sure most people here have heard about the microwave "invisibility cloak" that was made with metamaterials. For those that haven't heard, basically electrodynamics can be rewritten to handle changes in refractive index of materials with GR like tools where instead the background is...

Applying Newton's 2nd law?! Homework Statement A 2.91 kg block starts from rest at the top of a 32◦ incline and slides 1.98 m down the incline in 1.28 s. The acceleration of gravity is 9.8 m/s2 What is the acceleration of the block? Answer in units of m/s2 What is the coefficient...

Homework Statement A man standing in an elevator that is moving with a constant acceleration holds a 3-kg block B between two other blocks in such a way that the motion of B relative to A and C is impending. Knowing that the coefficients of friction between all surfaces are μs = 0.30 and μk =...

Homework Statement There is a box on a platform with mass 3.5kg and it has two ropes connected to it. On the end of each of these ropes are 2 other boxes hanging off the table (so only F_y component). One box is 2.5kg and the other is 1.5kg. I need to find the acceleration of all the boxes...

Suppose A box represents the universe. It also has a battery and a propellor inside it. The propellor is supposed to increase the temperature of the whole universe including itself and the battery. If this hypothetical universe is initially at 25 degrees C, then we incresed this temp to 27...