Rest Definition and 558 Threads

What exactly do we mean by rest energy of a particle ? It is known that electron has rest energy of .511Mev but what is meant by this ? An electron is never at rest (except in its own frame of reference) then why it is said rest energy ?

Please help! i know how to do a elastic collisions in 1 dimension, but the 2D is too confusing...here is my problem: You have a blue ball with a mass of 1.5 kg moving with a speed of 4.5 m/s in a direction below the positive x-axis. You have a red ball with a mass of 3.6 kg moving with a...

Homework Statement For a car starting at velocity=0 m/s, what would limit the acceleration in the first fraction of a second? (It's isn't the power of the engine) Use the fact that the force acceleration the car is the power over the velocity minus the air resistance force. The drag...

This concept would be dependant on having the technology to actually travel at velocities which we can now, only impart to particles Ie: .99c The plan would be to have 3 ships somewhere in space with negligable gravitational effect. 2 of the ships set out in opposite directions...

Homework Statement A moving 2.3kg block collides with a horizontal spring whose spring constant is 258 N/m. The block compresses the spring a maximum distance of 0.09m from its rest position. The coefficient of friction (mu) between the block and the horizontal surface is 0.32. What is the...

Homework Statement A charge q of mass m is released a distance d from a semi-infinite grounded conductor. How long will it take the charge to reach the conductor? So I tried this using the method of images, and I can easily find the force on the charge a distance d away: F = -q^2 zhat /...

Homework Statement So this was part of a two part thing, the first part was just to find out which statements were true and i figured that out but as far as this i just don't know what to do. this first stuff is for the problem that i already have and it is the second stuff that i need the...

Homework Statement A 2.80 kg mass, m, on a frictionless table is moving in a circle with radius 0.440 m at a constant speed. m is attached to a 5.40 kg mass, M, by a cord through a hole in the table. Find the speed with which m must move for M to stay at rest. for this one i am completely...

Homework Statement Electrons in a TV tube are accelerated from rest through a 25-kV potential difference. With what speed do they hit the TV? V = 25*10^3 J/C Homework Equations I'm not really sure here. I'm thinking you have to use Newtonian mechanics somewhere here. So, x(t) =...

Has anyone noticed that all candidates have blue sites? http://www.barackobama.com/index.php http://www.johnmccain.com/ http://www.hillaryclinton.com/ And, they all are so similar. I liked Obama's one. It is brighter than others.

Anyone can help me anayst the beariing which rest on the rod and was betweeen rod and ceiling...I am not sure if the reaction is between bearing and rod or ceiling and ball bearing. refer to this link pls

Is it the case, that in general relativity the rest length is not absolute? How is the rest length defined? Is it the problem, that it is not clear how one should choose the rest frame of some object, if the object is large?

Suppose we have a box at rest that is filled with a uniform gas. We denote the volume by V and the pressure by p. Suppose next that we apply a small force to the box and accelerate it until it has a speed v. The key question is: Is it harder to accelerate the gas because it takes work not only...

In the article "Why does light have invarient speed?" on PF (first URL in attached file), there is a statement that for photons, m_0 = m \sqrt{1 - \frac{v^2}{c^2}} is 0 since v = c. (I'm not sure if the author is stating this or quoting somebody else.) Is this a valid...

Take this case: A person sleeps for four or so hours and there's another person who lies down for four hours but he cannot sleep, yet he rests. What's the real difference? The person who has slept feels fresh after getiing up which the other person feels heavy and fatigued. Why? Should we...

I am looking for an expression for the total energy of a particle of rest mass m_0 that includes kinetic and gravitational potential, if there is such a thing. If I take the product of the time-components of the four-velocity and four-momentum vectors, I get m_0 c^2 \gamma^2 where...

I understand photons have no rest mass, but I also learned in my physics class p=h/(lambda), and that mass depends on the frequency, my question is why can't something moving at c have rest mass if it can have... momentum I suppose is the term...

Homework Statement How much would the rest energy of a 1.0 Kg mass cost at the typical utility rate of $0.60/ kWh? Homework Equations E=mc^2 The Attempt at a Solution Heres what somone told me from another website: "The rest energy of a mass is the energy calculated by E=mc^2...

Homework Statement A 2.5 kg block is on a 53 degres incline for which Uk = 0.25 and Us = 0.5 . Find its acceleration given that (a) it is initially at rest. I don't know how to approach this. We have kinetic friction when an object slides. This object starts at rest. Does that mean...

1. Ok, I've been working on this problem for ever and it seems easy but I know that there is something wrong. A vessel at rest explodes, breaking into three pieces. Two pieces, having equal mass, fly off perpendicular to one another with the same speed of 90 m/s. One goes along the negative...

Theoretically, if an object were to have negative rest mass, would it travel faster than light?

Hello, I'm working on this problem and I'd like to know how to find the invariant mass using just the lab-frame momentum and rest mass. I've found a lot of equations that deal with E, and I'm not completely sure what that is either. Thanks

Starting from rest several toy cars roll down ramps at different lengths and angles. Rank them according to their speed at the bottom of the ramp from slowest to fastest. Car A goes down a 10m ramp inclined at 15 degrees, Car B goes down a 10 m ramp inclined at 20 degrees, car C goes down a 8...

Homework Statement What should be the spring constant k of a spring designed to bring a 1440 kg car to rest from a speed of 111 km/h so that the occupants undergo a maximum acceleration of 5.0 g? ____N/m Homework Equations F=-kx F=ma V2=v(initial)2 + 2a(x) v=v(initial) + at The...

Hello, I'm having trouble finding the rest energy of delta, on the internet. Can anyone give me this value please. It's delta zero. i.e. its charge is 0 and strangeness is 0 too. Thanks a lot for your time From Steven

You are driving to the grocery store at 20 m/s. You are 110m from an intersection when the traffic light turns red. Assume that your reaction time is 0.50s and that your car brakes with constant acceleration. How far are you from the intersection when you begin to apply the brakes? What...

Fluids at rest problem help! Homework Statement How much force does it take to hold 0.5 m^3 of medium density (specific gravity = 0.77) wood under water? The Attempt at a Solution density of wood is 770 kg/m^3. Fb is the force of buoyancy that pushes the wood up. F-Fb = mg...

I had a conversation with my nuclear physics professor and she got mad bcs of me. I claimed there's no pi meson in the nucleus and i know a calculation (which is completed by Yukawa) that predicts an exchange particle mass about 100 MeV but a pion has a mass about 140 MeV. So I claimed that...

Suppose the neutron decay time n was 89 sec. AND the difference in rest mass between neutron to proton, Qn, was 0.129 MeV. What would the maximum Helium fraction, Yp, be?

1. A ball of mass m is projected with speed vi into a barrell of a spring gun of mass M initially at rest on a frictionless surface. The ball sticks in the barrel at the point of maximum compression of the spring. no energy is lost in friction. a) What is the speed of the spring gun after the...

A cue ball (mass=0.165kg) is at rest on a frictionless pool table. The ball is hit dead center by a pool stick, which applies an impulse of +1.50Ns (Newton-seconds) to the ball. The ball the slides along the table and makes an elastic head-on collision with a second ball of equal mass that is...

Homework Statement Auto companies frequently test the safety of automobiles by putting them through crash tests to observe the integrity of the passenger compartment. If a 1000. kg car is sent toward a cement wall with a speed of 14 m/s and the impact brings it to a stop in 8.00 * 10^-2...

How can cosmology set an upper limit on the rest mass of neutrinos if we know that the universe contains about 450 neutrinos per cubic centimeter?

Homework Statement Traveling at a speed of 58.0 km/h, the driver of a car locks the wheels by slamming on the brakes. The coefficient of kinetic friction is 0.720. How far does the car skid before coming to a rest Homework Equations f=ma? uk=Fk/Fn ?? The Attempt at a Solution i...

Homework Statement 650kg elevator starts from rest. It moves upward for 3.00s with constant acceleration until it reches its cruising speed of 1.75m/s. What is the average power of the elevator motor during this period? Homework Equations use either force or conservation of energy...

Homework Statement A car starts from rest at a stop sign and accelerates to speed 15m/s in a time of 6 seconds. The mass of the car is 300kg and the mass of the rider is 100kg. What is the force on the rider? Homework Equations I figured the acceleration to be 2.5m/s/s. And I know that F =...

Homework Statement http://img337.imageshack.us/img337/2514/diagramfn4.png The Attempt at a Solution \sum F_{x} = w_{x} - T = m_{x}a T = (6.9)g - (6.9)a \sum F_{a} = T - w_{a} - f_{s} = m_{a}a T - m_{a}g - m_{a}a = f_{s} (6.9g - 6.9a) - m_{a}g - m_{a}a = f_{s} I don't see a 5kg...

If we can't find a frame of total rest, how can we calculate a rest mass?

Homework Statement (a) A box is placed on an frictionless inclined plane with an angle of 18° from the horizontal. The box has a mass of 35 kg, what is the magnitude of the acceleration of the box along the inclined plane? (b) What magnitude of force would you need to apply to the box in...

What is the rest mass m of a particle traveling with the speed of light in the laboratory frame? i believe m = (E² - (pc)²)^.5 / c² is the correct equation to use? as velocity goes up, so does energy and momentum? so when velocity is at speed of light, E = infinity and momentum = infinity...

Homework Statement A rocket moves upward, starting from rest with an acceleration of 29.0 m/s^2 for 8.00 s. It runs out of fuel at the end of the 8.00 s but does not stop. How high does it rise above the ground? (in meters) Homework Equations deltaX=(1/2)final velocity * change in...

Homework Statement Two people are standing on a 2.3 m long platform, one at each end. The platform floats parallel to the ground on a cushion of air, like a hovercraft. One person throws a 6.9 kg ball to the other, who catches it. The ball travels nearly horizontally. Excluding the ball...

If I had a perfect fluid I could write the stress energy tensor in the rest frame of the fluid as a nice diagonal tensor with [rho,p,p,p] and use this to solve the field equations. Pressure is just random internal motions, so what happens if all the particles in my perfect fluid decide to...

Homework Statement The plane of a 20cm x 20cm metal loop with a mass of 10g and a resistance of 0.010 ohms is oriented vertically. A 1.0 T horizontal magnetic field, perpendicular to the loop, fills the top half of the loop. There is no magnetic field through the bottom half of the loop. The...

Homework Statement So the concept is, you've got a very large slab of stone. For arguments sake, let's say it's about 8 feet high, 4 feet across, and 2 feet thick. How much force would it take to push the slab over, pushing at the top for maximum torque. If granite weighs about 165...

An electron is released from rest at the negative plate of a parallel plate capacitor. The charge per unit area on each plate is σ = 1.69E-7 C/m2, and the plates are separated by a distance of 1.72E-2 m. How fast is the electron moving just before it reaches the positive plate? i started by...

Bullet is fired at a block resting on a table. The velocity of the bullet is 390 m/s and has a mass of .007kg. The mass of the block is .850kg. The bullets penetrates the block and exits it with a velocity of 130 m/s causing the block to slide a distance of .410 m. What is the coefficient...

I have been reading from this forum 2-3 years and officially became a member recently. Another member and friend, now also passed, had said to me selfAdjoint's posts were worth attention. Many times too much for me to understand them, yes. So I will speak for two, Mr. Bolontiku (BoulderHead)...

Homework Statement a 3 gram bullet traveling at 350m/s squared hits a tree and slows down uniformly to a stop while penetrating a distance of 12 cm into the tree's trunk. What was the force exerted on the bullet bringing it to rest? Homework Equations The Attempt at a SolutionI...

The mass of sun is determined by measuring the distance of a planet from the sun,the speed of that planet around the sun ,and then using Newtons law of gravity.In the same fashion one can determine the distribution of mass in a galaxy by observing the position adn motion of the stars in that...