Conceptual Definition and 874 Threads

Homework Statement Three building materials, plasterboard [k = 0.30 J/(s m Co)], brick [k = 0.60 J/(s m Co)], and wood [k = 0.10 J/(s m Co)], are sandwiched together (as I've tried to show below). The temperatures at the inside and outside surfaces are 28.9°C and 0°C, respectively. Each...

Hi everyone Thanks for viewing this thread. Hope it's in the right forum. I have some questions on basic mechanics that could really do with some clarifications, so I'd really appreciate any help you could provide. 1. Consider a ball with sufficient initial speed such that it moves in a...

Homework Statement 1.) When we collect more data for our confidence interval (A) Confidence Increases (B) Confidence Decreases (C) n decreases (D) The length of the interval decreases (E) The length of the interval increases 2.) We wish to determine a confidence interval for the population...

When I'm doing the Physics homework the problem for heat of vaporization uses Q=mcΔT and Q=mLv. How do I know when to use which equation through out the problem?

Homework Statement Find the volume: Prism formed by x+z=1, x-z=1, y=2, y=-2, and the yz-plane. Homework EquationsThe Attempt at a Solution Okay, so I sketched the drawing and I found that I could take the upper region of the xy-plane with respects to x and z and a triangle was formed. The...

I have a conceptual question. There is a law in science for every phenomenon in nature, like gravity or electric field. But also there are laws for springs or capacitors etc... I mean the engineering materials that are produced by engineering processes, not can be found in the nature itself...

Homework Statement Purely a conceptual/ terminology question, a simple yes or no will suffice :) In circular motion, will a point on its circumference will have a LINEAR acceleration which can be broken into two components- the RADIAL component which is v2/r and the TANGENTIAL component which...

When reviewing Electric field I had some confusion as to what the subscripts on [F][/0] and [q][/0] mean. Also what are we calculating here? I know its the electric field but what does this term mean?

Here is the question that we have been debating for the past day or so: Take a conducting cubic box and center a conducting sphere with charge +q inside of it. Will the induced charge density on the sphere be uniform or not?My gut instinct is no. The cube and sphere have different symmetries...

Homework Statement [/B] If the speed was doubled, what would the radius and period be to keep the same acceleration? Homework Equations a = v^2/R T = 2piR/tThe Attempt at a Solution So with my understanding it is as follows: (2v)^2/R This makes it 4v^2/x = a since a=v^2/R Setting this into...

Homework Statement The lightweight pivoted bar in the figure will be in rotational equilibrium when a 200N force acts (a) down at D (b) up at B (c) down at E or up at C (d) up at C only (e) none of these Homework Equations Torque = Force x Distance ∑Torque= 0 for rotational equilibriumThe...

Homework Statement 3. A bird feeder of large mass is hung from a tree limb. A cord attached to the bottom of the feeder has been left dangling free. Curiosity gets the best of a child, who pulls on the dangling cord in an attempt to see what's in the feeder. The dangling cord is cut from the...

Let ##L(\vec{r},\dot{\vec{r}})## be the lagrangian function, usually to get angular momentum conservation one impose ##\delta L=0## and form there we get ##\sum \vec{r}\wedge m\vec{v}=const##. There is however a conceptual problem with this procedure related to the fact that invariance under...

Hello everyone,I've been going through my school's freshman physics course pretty smoothly, but momentum seems to be a difficult concept for me to master. I understand all the equations and how the variables relate to one another, but we've gotten to the law of conservation of momentum and a lot...

Hi everyone, I am a High School student (final year) and am doing an extra-curricular project. Having complete autonomy on what we do the project on, I choose to design a High-Altitude Long-Endurance (HALE) UAV, such as the QinetiQ Zephyr [http://www.airforce-technology.com/projects/zephyr/] or...

Homework Statement Find the accelerations of each of the following three blocks: 2kg block, stacked on top of a 3kg block, stacked on top of a 7kg block When a force of 10N is applied on the 2kg block. Given: Coefficient of friction between 2kg and 3kg block is 0.2, coefficient of friction...

NOTE: The following questions are not part of any homework assigned. This is part of finding extra concept-related questions to help me study for my physics unit test. Homework Statement I have conceptual questions, not problems. I'll provide sufficient evidence that I've attempted to think...

please note- (GEM forces) stand for gravitational or electric forces. Under normal circumstances, we are not aware of the gravitational or electric forces between two everyday objects. Is this so because of the relative mass of these objects are very small in magnitude, when compared to larger...

Homework Statement A mass hangs from the ceiling of a box by an ideal spring. With the box held fixed, the mass is given an initial velocity and oscillates with purely vertical motion. When the mass reaches the lowest point of its motion, the box is released and allowed to fall. To an observer...

Guys, i really need help on answering this question... Can a charged particle ever move from a low electric potential to a high electric potential and yet have its electric potential energy decrease? Explain. What i think is that, no it is not possible for a charged particle to move to a...

As i understand, the induced current in a wire equals -d(∫∫B⋅dS)/dt What is S? I know it has to be an open surface for the flux integral to be non-zero, but over what surface do i do the integral?

I've taken up to the equivalent of first year undergrad mechanics, but this simple concept is unclear to me. Say a force F is applied (perpendicular) to a rod (in a vacuum with no gravity-- F is the only external force) at a non center of mass point A for a tiny time dt. How does it move...

A penguin floats first in a fluid of density p0, then in a fluid of density 0.95p0, and then in a fluid of density 1.1p0. a) Rank the densities according to the magnitude of the buoyant force on the penguin, greatest first. b) Rank the densities according to the amount of fluid displaced by the...

Is the air pressure acting on the top of the head of a person standing in a room equal to the air pressure acting on a same area on the floor of the same room? Since F = pA , it seems as if the air pressure is independent of the height of the surface on which it is acting. But that doesn't seem...

Homework Statement Find the components of all forces acting on member ABE. Homework Equations Equations I used are on attachment The Attempt at a Solution I found moments about E and F. My reaction at E is correct. I just have a conceptual question about the reaction at C. The reaction is a...

Homework Statement A student holds a book at rest on the palm of her hand. She lifts the book straight up, bringing it to rest again at a higher point. 1. Is the net work done on the book positive, negative, or zero? 2. Is the change in the gravitational potential energy positive, negative...

Hi, I am trying to wrap my head around what happens when a ball of mass m bounces against a hard floor. I assume a system that includes the ball and the floor (and eventually the entire planet) and an elastic collision. Before the ball hits the floor it has a momentum of mv. After the bounce...

Homework Statement A metal ring of mass m and radius R is placed on a smooth horizontal table and is set rotating about its own axis with a constant angular speed ω. What is the tension in the ring ?Homework EquationsThe Attempt at a Solution Consider a small element ds=rdθ .Tension T acts at...

The question is: A turtle is on a turntable. which is rotating on frictionless bearings at an angular velocity omega. The turtle walks towards the outside of the turntable (away from the center). Which of the following is true about the system's angular velocity omega and its angular momentum...

Homework Statement What is transactional acceleration? Homework EquationsThe Attempt at a Solution I have been looking for it all over the internet and I can not find an explanation for it that is easy to understand

I'm confused by classic description of work and negative work. If someone pulls (slowly) on a rope to lift a bucket in a well, I understand that the person is doing work on the bucket and gravity is doing negative work on the bucket. So, the net work is zero. But if the net work is zero...

Homework Statement [/B] Why does it take longer to cool water in a refrigerator than it takes to cool air, assuming that the inside of the refrigerator is initially at the same temperature as the room it is in? Homework EquationsThe Attempt at a Solution Quite frankly I don't even know if my...

Homework Statement Not hw.. My teacher wants us to understand this as it is important for reactor design. A liquid is flowing through a tube of diameter D. The inner wall of the tube is maintained at a constant temperature of Ts. The liquid enters at a temperature of Tw1and leaves at a...

My question isn't a homework question, it's a general conceptual question. We were going over a "work" problem in class and our professor told us that the work required to lift an object up to a certain height was equal to "mgh". However, is this only the case when we assume that acceleration is...

Homework Statement "Normally, jet engines push air out the back of the engine, resulting in forward thrust, but commercial aircraft often have thrust reversers that can change the direction of the ejected air, sending it forward." "When might thrust reversers be useful in practice? (Chose all...

Hi, So I'm working through a bunch of problems involving gradient vectors and derivatives to try to better understand it all, and one specific thing is giving me trouble. I have a general function that defines a change in Temperature with respect to position (x,y). So for example, dT/dt would...

Hello! I have a few conceptual questions regarding thermochemistry. In thermochemistry, why is Q of solution equal to negative Q of reaction? Why is a volume decrease equal a POSITIVE value for w?

I am losing my mind over this, it seems the longer i think about it the further i get from a definitive answer. It started with me trying to understand the variables the would result in a standing wave, ie: what needs to occur, why, and how it occurs. At first i was confused because it seemed...

Homework Statement Figure 21.13a shows the bubble-chamber tracks resulting from an event that begins at point A. At this point a gamma ray (emitted by certain radioactive substances), traveling in from the left, spontaneously transforms into two charged particles. There is no track from the...

Homework Statement [/B] A 30 kg girl standing on slippery ice catches a 0.5 kg ball thrown with a speed of 16 m/s. What then happens to the girl? Homework Equations F=m*aThe Attempt at a Solution Assuming that the ice is completely smooth (zero friction) then… F = m x a F = 0.5 kg x...

Hello! I'm a high school teacher in physics. I will teach Newtons third law this coming week and found the following question (regarding a horse pulling a carriage): "If the force on the carriage is equal and opposite to the force on the horse how can the horse pull the carriage? Is the...

Question:A bicyclist starts from home and rides back and forth along a straight East/West path. Her (instantaneous) velocity as a function of time is given by v(t), where time t is measured in minutes. Consider: d_{1} = \int^{30}_{0} v(t) dt and d_{2} = \int^{30}_{0} |v(t)| dt Choose what...

Hi, I'm hoping to clear up a few uncertainties in my mind about proving that the identity element and inverses of elements in a group are unique. Suppose we have a group \left(G, \ast\right). From the group axioms, we know that at least one element b exists in G, such that a \ast b = b \ast...

How can my cell phone WiFi antenna reach my far-away router with a small antenna but the router needs a large antenna to reach the same distance? Do the Wi-Fi/radio signals from my cell phone antenna have to reach my Wi-Fi router to connect to it or do the radio signals have to meet in the...

Hi all, I have a (hopefully) quick conceptual question that I'd like to clear up with your help. Is the following argument for why we treat position and velocity as independent variables in the Lagrangian correct? (referring to classical mechanics) : The Lagrangian, \mathcal{L} of a given...

Hi guys, Sorry if this isn't quite the right place to post this, but I have a few conceptual questions that I'd like to clear up about time evolution of a quantum state. Firstly, what is the exact argument for the evolution operator \hat{U}\left(t,t_{0}\right) being independent of the initial...

Homework Statement A hoop sits on a bus. The bus begins to accelerate toward the right with acceleration a1, shown below. The bus tires do not slip on the road. As the bus accelerates, the hoop begins to roll without slipping on the rigid floor of the bus and has rightward center of mass...

Hi all, I recently came upon the following problem in Giancoli's Physics Principles With Applications, 6th ed. textbook that I am having some issues understanding. I am new here, so I do apologize if I have made any mistakes in formatting or anything else. Homework Statement A 0.140-kg...

I have six weeks (19 school days) to teach half-a-course worth's of material to the students who failed Conceptual Physics. I have five days to teach: What is physics, the concepts and some basic problems of linear motion, and all three Newton's laws. Alas, the first three days haven't...

Homework Statement Two boxes of masses m and 3m are stacked. The surface between the more massive box and the horizontal surface is smooth and the surface between the boxes is rough. If the less massive box does not slide on the more massive box, what is t he static friction force on the...