# Tagged Questions

Scalar quantity which is the magnitude of velocity.

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### Does travelling towards something at relativistic speed cause it to appear to speed up?

If one were to travel towards a giant TV floating in space, at a fraction of the speed of light, would a video playing on the TV appear to play faster? I'm guessing the answer is no. From what I ...
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### Difference between Speed and Velocity

What is the difference between Speed, Velocity and Acceleration? Could any one describe it pictorially?. I am more over confused even after investigating many times. I am unable to relate myself ...
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### Is there a maximum energy for a relativistic particle?

So I was told today that the Standard Model breaks down at really, really high energies. The lecturer mentioned particles such as electrons hypothetically having energies equivalent to that of entire ...
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### Can a tomato pierce a hole in a steel plate if only the tomato is travelling fast enough?

A tomato is travelling very fast towards a 1 cm thick steel plate. Let's say this happened in a vacuum, so that the air resistance wouldn't rip the tomato apart before it even hit the steel plate. ...
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### How fast does the water have to go? [closed]

I have a pot of water. There is a one-way filter at the bottom right: How fast would the water have to be travelling to go into the tank via the one-way filter? Also, I would like to have some ...
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### If a car is travelling faster than the speed of light, do the headlights still work? [closed]

If a car is travelling faster than the speed of light, do the headlights still work? If you can help because i really need to know i am going on a trip with my car tomorrow!
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### Can light projection on a wall travel faster than the speed of light? [duplicate]

If I project a flashlight beam on a wall and turn the source, the projection (as seen on the wall) is seen moving along the direction of the turn with some speed. If I have projected it on a gigantic ...
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### Something almost faster than light traveling on something else almost faster than light [duplicate]

Possible Duplicate: Travelling faster than the speed of light Double light speed Lets say that an airplane can fly at 4/5 of the speed of light, and I can run at 2/5 of the speed of light, ...
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### How to calculate the diameter of a moving circle from afar while lacking and knowing some information?

Let's say there is a solid wood wheel with two tires attached at the bottom travelling on a level road towards me while facing me width-wise (as in, the side of it from which you can see its diameter)....
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### Can motion be characterized without time as independent variable? [closed]

I was just thinking about speed = distance/time which relatively describes how fast something is moving wrt some still object. So if by some wishful thinking or some coordinate system I remove the ...
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### Is escape velocity really a velocity (rather than a speed)?

The term escape velocity is quite common to us. But we know velocity is a dimension dependent on the direction. But the escape velocity has same value irrespective of from where it is thrown from the ...
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### Why can't we use this method to achieve extreme speeds?

Turn an axle with diameter 1 inch at 1 mile per hour, and an attached wheel with diameter 5 inches will spin at 5 miles per hour. Why can't we apply this principle on a much bigger scale? Say you put ...
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### Can absolute speed be determined by an object's mass?

It's been said that nobody can actually know how fast the Earth is moving through space, because a reference point is needed to determine absolute velocity. But if mass increases as speed increases, ...
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### Why is this result wrong for finding speed of a neutron in relation to deBroglie wavelength [duplicate]

So given a deBroglie wavelength 1.8nm and the equations E=hf and E=1/2mv^2 you can get v = 2h/m*(1.8*10^-9) but this is 2 times the expected value. Wherever I look online people use the momentum p ...
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### How fast does a long object bent at the center need to be travelling in order to boomerang?

At an angle, of course. Standard pressure, average temperature, and calm wind. Bonus question: Can an object that is not bent boomerang at all? If yes, how different would the equations for this ...
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### Faster alternative to travel to any location in the west? [closed]

Suppose one needs to travel to Somalia from Indonesia(which are approximately at a distance of $4000$ miles from each other on the line of equator). To accomplish this task, I suggest the following ...
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### Field of view from travelling at (almost) the speed of light?

As we go faster, our field of view increases, but would happen if we travelled at (almost) the speed of light? My questions: Can we see a 360 degree view while travelling at (almost) the speed of ...
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### Impossible? Or not? [closed]

If the universe is expanding at light speed, and you stand on the edge moving out, if you look across the universe, then you will see twice the light speed, why is that?
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### Power vs. Speed - Indoor rowing

In the sport of indoor rowing (and probably others) I know that to double your speed you must increase your power output by a factor of eight. I am wondering why this is the case. The indoor rower ...
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### Why did they use two separate vectors to calculate the magnitude and angle of the initial velocity?

The question/solution are on the attached images. (It's dealing with projectile motion) I already understand how to work out part a, but I'm having trouble understanding why they used the final ...
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### Calculating speed of an object at the bottom of a curved slope? [closed]

Say you had a slope and it was like a ski slope that started shallow, got steeper and shallow again, and you knew that the top of the slope was a certain height vertically upwards from the bottom of ...
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### How should speed be expressed in Frenet-Serret frame of reference? [closed]

I'm looking for the equation of motion of the ball on a vertical plane with a cylindrical profile. I guess that means I have to use the frame of reference of Frenet-Serret here. Why is the speed of ...
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### Time taken to cover a point object in a circular region

I'm assuming a finite width rotating beam with increasing width as it gets closer to the circular edge. I'm trying to find the time it takes the beam to cross a point object at some distance from the ...
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### Why is the speed of sound lower at higher altitudes?

At sea level the speed of sound is 760mph, but at altitudes like the Concorde would fly at (55,000ft) the sound barrier is at 660mph, so 1000th slower. Does it have to do with lower pressure?
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### What is meant by 'Phase velocity is $c^2/v$' [closed]

Is phase velocity $c^2/v$ or $v/2$? Is there only one phase velocity as indicated by the above formula? If yes then why is wavepacket said to be superposition of 'waves' whose velocity is termed as ...
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### How fast are we moving when standing still? [duplicate]

The Earth rotates around itself and revolves around the Sun. Our solar system revolves around the center of our galaxy and our galaxy is moving in some way throughout the universe. If you took into ...
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### At What Point Does Mass Cease to Matter?

I know very little about physics so I naturally have a lot of simple minded questions. Assuming I am piloting a rocket and want to obtain the fastest speed possible. At what point does mass more ...
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### Speed and multiple images

Why an object (or something else) create multiple images of itself when it is moving fast? An earphone spinning in circle for example.
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### Objective velocity (Relativity theory) [closed]

Suppose that I have a velocity of (approximately) $c$. Then I decelerate with $c$ per hour for exactly one hour. Then I would know that I would be standing still in the end, because the decelleration ...
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### Why does the wavelength gets shorter in the denser medium in refraction? [duplicate]

In the refraction, the wavelength gets shorter if it enters denser medium. Why is that happening? Is it just a phenomenon?
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### Difference between escape velocity and speed [duplicate]

What is the difference between escape velocity and escape speed , is their any error if we use them interchangeably?
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### Question about acceleration & deceleration in real world?

have searched the net and am not satisfied with any answer I have found to calculate the following:- Here is an example just for reference. Suppose I can accelerate my car from 0-100km/h in 10s. That ...
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### Speed Calculater [closed]

I want to make an android calculator which can calculate speed of a vehicle by using mobile sensors(accelerometer or GPS) i am interested to calculate it by using accelerometer instead of GPS is it ...
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### Calculating speed of satellite in vacuum?

Satellite speed is $35\ \mathrm{km/s}$ after burn for $500\ \mathrm{ sec}$ and after some days or months this speed is reduced automatically $34$, $33$, $32$ respectively. Questions: How the ...
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### Can a human size object move so fast that it ceases to be observable?

In many anime, comics, movies, etc, we see a lot of super human beings moving and fighting at such high speeds that a regular human being cannot see that they are fighting or moving pass by. In ...
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### Can rotating disk clocked at its center at the speed of light have an outer edge that travels faster than the speed of light? [duplicate]

I have been running this through my head for a few days and I understand I am probably missing something very simple here. If a wheel is spinning the outer edge will travel at a speed that is greater ...
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### Behaviour of gases in a vacuum

I have a doubt related to the behaviour of gases in a vacuum. In the following figure: The grey part is the vacuum and the green part is the gas, let the gas be Carbon Monoxide. The following are ...
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I’m a writer. I'm working on a story. It’s sold actually, but they want some changes and I’m trying to figure out the science.. IDEA: A distant planet picks up broadcasts from Earth, so the ...
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### How do radar speed signs work?

Everyday when I'm going back home from college, I pass by this big radar speed sign and I've noticed that it does a peculiar thing. The sign is placed on a downward slope of the street. So say I'm ...
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### Escape speed or Escape Velocity? [duplicate]

Which one should be the correct term escape speed or escape velocity? In one book it is given Speed whereas in another its velocity.
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### What happens if a motorcycle going at 50mph crashes head into a car going at 60mph? [closed]

I wonder if a motorcycle (going at 50mph) crashes into a car (going 60mph), what is the damage that motorcycle will experience? Here's a diagram that shows what I've in mind: ...
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### Speed as the fifth dimension

In spacetime there are four general dimensions, three of space and one of time. Why is it that other dimensioned qualities seem to be rarely considered as part of spacetime? For example, why isn't ...
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### How fast would you have to run to create a mirror image?

So I was watching The Flash and in the most recent episode he runs so fast that he is able to create a mirror image of himself so that it looks like there is more of him than there actually is. So I ...
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### What prevents me to accelerate an object to near light speed in space?

As far my limited knowledge go, things in space aren't slow down unless something interferes with them, so what prevents me to build a spaceship powered by nuclear power that will keep accelerating ...
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### Initial speed in homework problem [closed]

This is a homework question. I tried to solve it, but failed. I had to translate this question, so please forgive me if it is poorly worded. In this question you can ignore the atmospheric ...
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### How can we see the alien, who are travelling in light speed? [closed]

If aliens has the technology to travel in speed of light ,How can we see them with our 'below the speed of light' technology?. Because when we see that(!),definitely it will not be in its place.Is ...