Questions tagged [relative-motion]

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If you are sitting completely still inside of a moving car are you at rest?

My teacher and I had an argument in class where I stated that motion is undefined without a reference point and that you could just as easily claim that the road is moving backwards at the opposite ...
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0answers
350 views

Question based on relative motion in two dimension

I came across this problem in my work book. A hunter is riding on an elephant of height $4$ $ m$ moving in straight line with uniform speed of $2$ $ m/s$. A deer running with a speed $V$ at a ...
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2answers
181 views

Inertial force in a bus [duplicate]

While i am standing in a bus that is accelerating an inertial force is acting on me in the direction opposite of acceleration (I understand that). But, what is the magnitude of that force.I thought it ...
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2answers
133 views

How can I visualize the center of mass (center of momentum) frame?

I know that the CM frame is the frame in which the total momentum of the system adds up to zero. For example, if I imagine two bodies m1 and m2, with m1 = m2, one moving at the speed v1 = v and the ...
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1answer
148 views

Physics of the tablecloth trick- why top objects tip over

In the tablecloth trick where the cloth is pulled off, with dishes etc. on top of it, I was wondering why is it that tall objects tend to tip forward? Let's say that we are pulling the cloth to the ...
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1answer
77 views

relative velocities

If two objects are moving relative to the horizontal and you have the real angle between the horizontal and the direction of travel of one object, how does this real angle differ from the angle ...
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0answers
60 views

Concern about Spacetime Invariance [duplicate]

The space-time invariance principle states that: $(c^2)(\Delta t^2) - l^2 = \rm invariant$ for any inertial frame. Consider two events that occur at the same time in inertial frame $S$, and frame $...
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1answer
63 views

Can the Doppler effect account for the increase in an object's energy with velocity?

I am aware that the relativistic mass can be expressed in terms of rest mass and momentum, which seems to be the canonical explanation, but I am looking at an alternative way of visualising the ...
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3answers
802 views

Relative motion involving angle

Suppose I am going in a direction with a velocity $v_1$ and my friend is going in a direction which makes an angle of $A$ with my direction with a velocity of $v_2$. Then what will be my relative ...
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3answers
200 views

Special Relativity - Why does time dilation cause length contraction? [duplicate]

As an object moves faster, its time runs slower by factor X. I get why this is the case, but I'm not sure why distance is decreased by factor X as well. Questions: 1) Why does a moving object's ...
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1answer
5k views

Why is Voyager 1 approaching Earth? [duplicate]

When I read JPL's mission status for Voyager 1 and Voyager 2 the distance between Earth and Voyager 1 is decreasing. Is it right?
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3answers
144 views

Inside a box moving with constant velocity

Suppose You were put into a box with all the instruments you might require. The box moves with constant velocity on the surface of the earth. We are asked to detect inside the box whether we are ...
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2answers
161 views

Can sound be faster than 300m/s?

If you sit in a car and it's driving $300{m \over s}$ and you clap your hands for a very very short sound, will it's wave be $600{m \over s}$ fast, because it adds the speed of the car? Or will it be ...
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3answers
159 views

Relative motion + electromagnetism

We say that Force exerted by a current carrying wire on charge $ q $ moving with velocity $v$ is: $F=qvB\tag*{}$ (Where $B$ is the magnetic field , and electric Force is 0 because wire is neutral.) ...
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2answers
112 views

Is it possible at half speed of light to explore in space or walk with suits like astronaut do? ( Passengers Movie )

In the film Passenger the spaceship was flying at half light speed so I was thinking was it even possible that like chris pratt one can go out of such fast moving ship with just the rope tied not ...
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3answers
176 views

Is probability relative?

Suppose you are as massive as earth and you are tumbling down space at a very high speed. You flip a coin. There is a probability function associated with the coin in motion. When it falls back in ...
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0answers
166 views

Relativity of simultaneity - under what conditions would two events happen simultaneously for frames $S$ and $S'$ when $S'$ is moving relative to $S$?

I feel like I have a fundamental confusion with the following exercise: I'm confident with my answer in (a), which is that $B$ must be within the light cone of $A$, or that $B$ is causally connected ...
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1answer
288 views

How to calculate angle between two objects going at relative velocity [closed]

I am having trouble with a relative velocity exercise. If any of you could bring some light on it i would be very happy. The exercise as it is on the book: The relative velocity of a butterfly and ...
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2answers
88 views

Relativity of velocity while riding a bike

I was trying to think of a situation in which an observer would be able to determine whether he is moving or not. Since velocity is a relative quantity I was unable to do so. However, consider a ...
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2answers
75 views

Direction of velocity

I found this question and I have a problem: Two friends A and B are standing a distance $x$ apart in an open field and wind is blowing from A to B. A beats a drum and B hears the sound $t1$ time ...
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4answers
157 views

Question about spinning Earth

The earth spins on its axis at 1674 km/h from west to east. Would it not imply that an airplane flying eastbound at 500 km/h would cover a distance of 500 kilometres in an hour while another plane ...
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1answer
34 views

Revolution of the Earth [duplicate]

Good day, it seems easy but I still find it difficult to understand why we return to the same spot when we jump despite the Earth revolving beneath us. Can someone explain?
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2answers
80 views

Does time really pass slower near massive objects or only if there is motion of a reference frame relative to it?

Question is fairly self explanatory. From relativity, we hear that the Earth distorts spacetime making the time pass slower near it in respect to an observer in outer space. My question is, if the ...
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1answer
476 views

Relative acceleration of one object to another [closed]

Cat A is traveling at a constant positive-x direction of 5m/s. Cat B is accelerating at a 0.5 m/s^2 on the positive-y direction. The question is: What is the acceleration of cat A relative to cat ...
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1answer
153 views

If Earth is curve and spinning, why plane flying in high altitude does not delayed?

If earth is spinning globe then the layer of athmosphere have a different tangential velocity for different altitude. For near the ground (solid surface of the earth) then the velocity of the air just ...
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2answers
240 views

Directions of static & kinetic friction?

Static friction : Static friction opposes relative motion between two surfaces. The car is moving at some tangential velocity relative to the road. Thus, static friction should act in the opposite ...
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1answer
60 views

Accelerating towards a photon

What will be the relative speed and motion between me and a photon if I would have accelerated towards a photon that is moving away from me? Would it get away from at a slower velocity relative to me, ...
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1answer
119 views

Relative velocities problem ; how to draw useful diagrams if more than 2 things are changing?

Two students are canoeing on a river. While heading upstream, they accidentally drop an empty bottle overboard. They then continue paddling for 1.9 h , reaching a point 1.2 km farther upstream. At ...
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1answer
699 views

What makes an object to be at rest?

We understand both motion and rest are relative. But me and my friends always discussing about this kind of thought experiment involving a single object (for example, a particle with mass or massless ...
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2answers
597 views

Moving in a box with constant velocity [duplicate]

How can a person trapped in a box figure out, without looking outside, whether the box is stationary or moving with a constant velocity? Is it even possible, considering the fact that the box is an ...
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1answer
70 views

Kinetic energy in different frames [duplicate]

I have an electric bike moved by a battery. I am at a train station with two friends. A flat train car platform passes by at $1 m/s$. The friend #1 jumps on it while the friend #2 remains at the ...
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1answer
714 views

Angle of reflection of an object colliding on a moving wall

Consider an object colliding elastically with an inclined wall (with much bigger mass than the object) as in picuture. The wall is at $45°$ and it is moving. $(A)$: frame of reference of the wall (...
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2answers
897 views

Relative motion problem [closed]

A man travelling in a car with a maximum constant speed of 20m/s watches the friend start off at a distance 100m ahead on a motorcycle with constant acceleration a. The maximum value of a for which ...
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1answer
159 views

To what extent is acceleration relative?

I realize there are answers to my question many places across the internet and many places on this site, but from what I have seen, most of them either involve terms I don't know or assume you can use ...
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2answers
292 views

Earth's rotation and a helicopter [duplicate]

Imagine a helicopter that took off from point A on the ground and goes vertically in the air to a certain fixed point B in the atmospheric area at a certain fixed altitude with enough fuel to stay ...
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1answer
86 views

Shift in reference frame argument in Spin-Orbit coupling

Assume a hydrogen atom with an electron $e^{-}$of spin and orbital about a proton $e^{+}$ of no spin. The spin of the electron produces a spin magnetic moment and its orbital motion produces a ...
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1answer
708 views

Angular momentum about a moving point

I was used to see the Angular Momentum Principle as: $\dot{\underline{H}_O} = \underline{M}_O^{ext}$ that is, the change in angular momentum equates the external torque w.r.t. a point $O$. Now, I'...
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1answer
74 views

Clear Pictures from a Distance

How are astronauts able to take high resolution photos of small objects on the Earth's surface while traveling at 25,000 feet per second without the image being blurred?
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2answers
106 views

Changing mass and relative motion

Sand is pouring vertically on a cart at J [kg/sec], from negligable hight. The cart is standing on top of a frictionless surface. What force F do we have to apply to the cart for it to move at a ...
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2answers
987 views

What happen when a helium balloon is floating inside a moving train?

Let's assume a helium balloon is suspended into the floor of a moving train. We already know how it will react during acceleration, deceleration, and constant speed as illustrated in figure no 1, 2, ...
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3answers
61 views

Reference Frames

I observe two cars approaching each other from opposite directions and measure as 40 mph and 30 mph, respectively. How fast is the 40 mph car moving according to the driver in the 30 mph car? ...
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2answers
101 views

I don't understand the meaning of $M_{\alpha\beta}$ in this equation

I don't understand the meaning of $M_{\alpha\beta}$ here in this equation, is it a matrix, or it is a function of a variable ?
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1answer
399 views

Does relative velocity also depend on the distance from which moving object is being viewed? [duplicate]

When we are in train, objects just close to trains like the adjacent track, electric poles and such close things appear to move very fast against the direction of the moving train.Further the ...
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1answer
79 views

What happens if you ride a bike on to a moving sidewalk?

If a person were to riding a bicycle on normal ground then ride onto a conveyer moving in the forward direction of the bicycle (like a moving sidewalk in an airport), would the bike slow down or speed ...
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2answers
130 views

Find the speed of the man [closed]

A man runs at constant speed to catch a bus. At the instant the man is $40$ metres from the bus, it begins to accelerate uniformly from rest away from him. The man just catches the bus $20$ seconds ...
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1answer
402 views

Inertial reference frames vs. non-inertial reference frames

I have a problem concerning the motion in different frames of reference. This example confused me: We've got a train which is moving and we declare the rail was our inertial frame of reference (with ...
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1answer
470 views

What is the speed of a swimmer in a river when he wants to travel the minimum distance?

The speed of the swimmer in still water is $v$ and that of the river is $u$ ($v>u$). He should travel at an angle $x$ with respect to the direction perpendicular to the river's flow, towards the ...
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0answers
232 views

How to derive relative velocity in two particle scattering?

While calculating the scattering cross section for one particle scattering we use the formula $$J_i=\rho v$$ where $\rho$ is the density of the incoming beam and $v$ is the velocity of the incoming ...
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1answer
1k views

Velocity of separation

Defining velocity of separation / approach , my textbook states that it is component of velocity of one body with respect to another along the line joining them . Why is it that it is the ...
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3answers
669 views

Swimming across a river [closed]

I have come across a physics riddle where 2 swimmers with same speed $c$ are competing against each other in a river, they start at the same spot, first swimmer (s1) is swimming distance $d$ up stream ...