Rest Definition and 558 Threads

Homework Statement In the image shown, two blocks hang on a pulley. Assume that m1 is the more massive block, and that the pulley is massless and frictionless. Take the initial case to be the instant just after m1 is released from rest, and the final case to be the instant just before m2 hits...

Homework Statement A lift ascends from rest with uniform acceleration of 4m/s², then it moves with uniform velocity and finally comes to rest with uniform retardation of 4m/s². If the total distance covered during ascending by the lift is 28m and the total time for ascending 8s respectively...

Hello, my problem is as follows I've tried finding the invariant mass of the positron and pion as follows M^2=(E_e+E_{\pi})^2-(\mathbf{p_e}+\mathbf{p_{\pi}})\\ =E_e^2+E_{\pi}^2+2E_eE_{\pi}-p_e^2-p_{\pi}^2-2\mathbf{p_ep_{\pi}}\\ =m_e^2+m_{\pi}^2-2(E_eE_{\pi}+\mathbf{p_ep_{\pi}})\\...

Homework Statement A tennis ball is dropped from a point 4.9 m above the ground. Every time it hits the ground, it bounces back to ¾ of its previous height. How long will the ball take to come to at rest? [ignore the time required for hitting the ground and turning back] Homework...

Wasnt it ? So I stumbled upon this fragment from wikipedia's photon page "Current commonly accepted physical theories imply or assume the photon to be strictly massless, but this should be also checked experimentally. If the photon is not a strictly massless particle, it would not move at the...

Homework Statement An object is accelerated from rest by a force of 32 N over a distance of 18 m. Calculate the kinetic energy of the object after 18 m Homework Equations KE = 0.5 • m • v^2[/B] The Attempt at a Solution I can't work out where ill be able to get the mass or the velocity...

It seems to me that there are many instances of 'initial stickiness' when you move an object. Pushing a book over a table for example might be initially hard due to adhesive forces to the table which have formed over time - a plastic coating forming some kind of seal with a varnish is the...

Hello, Could someone check my following statement: The proper distance between two spacelike separated events can be thought of as the rest length of a rod that connects both events in an inertial frame in which both events happen simultaneous. Thanks in advance!

1. is there a difference between 'rest mass' and 'invariant mass'? I thought there wasn't... To put it another way (or maybe this next question is a different question): 2. Is there a difference between the rest mass of a positron/electron pair, and the rest massa of a system containing two...

Homework Statement A block is at rest on a rough incline . The frictional force acting on the block, along the incline, is A) greater than the weight of the block. B) equal to the weight of the block. C) zero. D) less than the weight of the block. Homework EquationsThe Attempt at a Solution...

Electrons in a particle accelerator reach a speed of 0.999c relative to the laboratory. Is the rest energy of the electron equal to zero?

i read some where that four momentum of photon is null vector that's why photon have zero rest mass.but i cannot get it.please help

Hi I am trying to understand more about these terms. I am currently studying a course about relativity and cosmology, but I am finding the textbook (Open University) difficult to follow. Can anyone help me untangle and make some simple sense of these different terms? Thanks (I accidentally...

Hi I am trying to understand more about these terms. I am currently studying a course about relativity and cosmology, but I am finding the textbook (Open University) difficult to follow. Can anyone help me untangle and make some simple sense of these different terms? Thanks

I'm wondering, starting with an extreme example, what would happen if two masses accelerate away from each other towards the speed of light. Imagine we could do this very quickly like large hadron separator and the distance is short (in terms of light travel per time) and we compare this to an...

In all the places where Spin-Orbit interaction is discussed, the equations are derived by going to electron's rest frame and considering the interaction of nucleus' magnetic field with electrons spin magnetic moment. But from SR, we know that there as to be an explantion from the nucleus's rest...

The Attempt at a Solution It seems as though the rest point is at the ends of the pendulum swing. I know that the period of a pendulum is the time it takes the pendulum to make one full back-and-forth swing. I think this problem is wrong if the rest point means equilibrium point. Because then...

Homework Statement Could someone please let me know if this is correct? I'm unsure about matter always being conserved, does it change whether we're talking about Newtonian physics or special relativity? To me, matter is conserved regardless but maybe there is something I don't know...

Hi, i'm stuck on a mechanics problem where the initial conditions are a mass at rest on an inclined plane, but the forces are seemingly unbalanced. 1. Homework Statement A 5.17 kg box sits at rest at the bottom of a ramp that is 8.56 m long and that is inclined at 40.0◦ above the horizontal...

Homework Statement Suppose that a certain accelerator can give protons a kinetic energy of 200 GeV. The rest mass of a proton is 0.938 Gev/c^2. Calculate the largest possible rest mass M0 of a particle that could be produced by the impact of one of the high-energy protons on a stationary...

Homework Statement A car weighing 1940lb has lost its brakes and is unable to come to a stop. A police cruiser of 3900lb gets ahead of it so that the two cars are now bumper to bumper. The combined cars are now traveling at 60mph down a 15 degree grade slope. If the police cruiser can normally...

Homework Statement A 5.00-kg block is held at rest against a vertical wall by a horizontal force of 100 N. (a) What is the frictional force exerted by the wall on the block? (b) What is the minimum horizontal force needed to prevent the block from falling if the static coefficient of friction...

I was remembering the equation E=MC2. So as per me Rest Mass is nothing but Energy that is stationary. Am I right?

Homework Statement Consider a wedge of mass m whose upper surface is a quarter circle and is smooth. The lower part is rough. A small block of same mass is kept at the topmost position and the initial position is shown in figure. The block slides down the wedge. Find the minimum value of...

Homework Statement Car A is starting from rest and accelerating at 4.0 m/s^2, car B passes it, moving at a constant speed of 28 m/s. How long will it take car A to catch up with car B.Homework Equations d=Vot+1/at^2 The Attempt at a Solution Using the equation above, I used it for car A...

This is problem 1.16 from Kleppner & Kolenkow's Introduction to Mechanics. I didn't know whether to post it here or pre-university math. A sportscar, Fiasco I, can accelerate uniformly to $120$ mi/h in $30$ s. Its maximum braking rate cannot exceed $0.7g$. WHat is the minimum time required to...

Homework Statement An alpha particle (the nucleus of a helium atom) is at rest at the origin of a Cartesian coordinate system. A proton is moving with a velocity of v towards the alpha particle in the xˆ direction. If the proton is initially far enough away to have no potential energy, how...

Say we have a one dimensional chain of N mass points separated by springs of spring constant k. This system can be quantized? Let the quantized system above be at rest and let one of the end mass points emit a photon of energy E along the crystal axis. Will we get physics similar to he...

Can you explain please! thank you.

Homework Statement An electron is moving at 5.4 \times 10^5 ms^(-1) is brought to rest as it enters a region of lower potential. What is the voltage that brought it to rest? Homework Equations \Delta KE=1/2m(v_2)^{2} - 1/2m(v_1)^{2} = W = -\Delta U = q \times \Delta V The Attempt at a...

Homework Statement A Truck is going around a circular track of radius 72m and is banked at 60 deg. A spider is at rest on the side of the truck and the coeffiecient of friction is 0.91, what is the maximum velocity of the truck so that the spider is at rest. Homework Equations F =...

I'm a high school chem and physics teacher, participating in a recreational online chem course hosted by MIT. One of the practice questions in this course asked how many atoms a certain mass would contain at 300K. This got me thinking about mass-energy equivalence, and whether the atomic...

I was going through De Broglie's acceptence speech and I found he said a particle at rest can be associated with a stationary wave. Now what We know wavelength= h/p(momentum). So for a particle at rest we get wavelength = h/0. This is undefined. So does not it state that a particle at rest is...

Force can be expressed as F = P/v where P = power (watts) and v = velocity (metres per second) So what happens when you use a given amount of power to accelerate an object from rest? This would be given by: a = P/(mv) And since v = 0 => a = P/(m*0) This would be division by 0...

Hey guys, as we know the concept of the rest frame is one of the most famous concepts in any kind of relativity, because it must be known in which frame the body is at rest. My question is how do we define a rest frame on a solid object that has atoms vibrating, the body clearly does not have...

Homework Statement A train is moving by a stationary observer, Bob, at 0.8c. An observer standing still in the middle of the train, Alice, measures the distance to each end of train as 9*10^11 m. Two lightning bolts hit each end of the train simultaneously, as seen by the observer at the...

Hi all. we know that the rest is the mass of an object within a coordinate system which has zero velocity, but how does it exist for an electron inside a crystal, which we call rest mass of electron, how electron exist with zero velocity.or we mean by zero velocity of electron with respect to...

A pendulum is released from rest at a distance y = H for the y = 0. What is the max velocity? \[ \frac{1}{2}mv^2 = mgh\Rightarrow v = \sqrt{2gh} \] where I assumed there was no air resistance. Would anything change if the system was in a vacuum?

... Three scientists are familiar with Special Relativity and it's rules. The three scientists decide to conduct a Special Relativity experiment. The plan is for two of them to get into two separate rocket ships and pass one another nearly head-on overhead while the third scientist...

Hi PF. This a fact well aware to just about anyone that has had even basic chemistry, but I'm having a hard time coming to an understanding as to why this must be true. So why? Also, if I knew that some box contained, say, a proton and an electron, could I ever know whether or not, inside...

so my given: s(t)=cos(pie8*t/4) took the derivative= velocity function then, v(t)= -pie/4 *sin(pie*t/4) When is the particle at rest? v(t)=0 now, 0= -pie/4 *sin(pie*t/4) im lost here. I know it's very simple I am just over thinking. What do I do from here? thanks

I, like many others, have always wondered whether photons truly massless or if their mass is just so small that its irrelevant? And of course, if they truly are massless, then how can black holes attract them? http://cosmoquest.org/forum/showthread.php?98056-Upper-limit-to-photon-mass <--...

I got the exam results for one of my most favourite subjects today-Dynamics of Machines,and it was horrible. Luckily I just managed to scrape through. In my university(German one),getting a very good grade is tougher than the University in my home town. I feel devastated because it was a oral...

The TOTAL energy of a pion is given, no other information is given so we don't know how fast it is moving, is it possible to calculate its mass? I'm assuming it's relativistic and we need GAMMA (the lorentz factor) Also if E is it's total energy what would it's kinetic energy be? wouldn't its...

Electrons emit and absorb photons all the time. I heard that each electron is surrounded by a cloud of 10^{20} photons. That suggests to me that the rest mass of an electron must fluctuate, and that raises the prospect of uncertainty. My questions: Is the rest mass of an electron really...

I was reading some posts on one of my previous threads (great discussion there btw) and I red something that I really didn't understand. So the basic premise was that if we have 2 clocks that undergo acceleration on the same level, to that they are mutually at rest, that they will see their...

Homework Statement A beam (red line) has mass m and length L. 3 chains are attached to the beam to keep it at rest. C1 which is perpendicular to the roof, C2 which is perpendicular at the center of mass on the beam, and C3 which is perpendicular to the side wall. Questions: Draw a free body...

The velocity of an object can, theoretically, only be measured relative to the velocity of another object. If I understand the concept of rest mass correctly, it is the mass of a particle with zero velocity; if my understanding is correct, what is 'zero velocity' relative to? Is it relative to...

A nucleus of rest mass m initially at rest in the lab absorbs a photon such that its total energy becomes 1.01mc^2. I've calculated the energy of the photon to be greater than the change in rest mass of the nucleus this is on track because the follow up question is why is the required energy...

Homework Statement True or False The stresses on an object traveling at constant velocity are the same as the stresses on an object.at rest. Homework Equations F = m*a The Attempt at a Solution For both an object at constant velocity and an object at rest the acceleration is...