What is Relative motion: Definition and 282 Discussions

The relative velocity







v
→




B
∣
A




{\displaystyle {\vec {v}}_{B\mid A}}
(also







v
→




B
A




{\displaystyle {\vec {v}}_{BA}}
or







v
→




B
rel
⁡
A




{\displaystyle {\vec {v}}_{B\operatorname {rel} A}}
) is the velocity of an object or observer B in the rest frame of another object or observer A.

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  1. A

    Creating black holes through relative motion

    My question is threefold, the second is based on the premise that the first is true, and the third is based on the other two. 1. As relative velocity increases, mass also increases, correct? In this case, could you accelerate away from an object to a velocity fast enough to make its...
  2. M

    Lengths perpendicular to relative motion are unchanged

    This has been bothering me for a long time. I can see that it's "obviously" true but I'm having trouble arguing it rigorously from what I know about special relativity (i.e. I "believe it" but when I try to (hypothetically) explain it to someone, I can't do so convincingly.) I first found...
  3. D

    Distance and displacement, relative motion

    1. The driver of a motor boat points it directly toward the opposite bank of a 52 m wide river. The speed of the boat is 4.0 m/s and the river flows at 3.2 m/s. When the boat reaches the opposite riverbank, what is the distance downstream from its point of departure? 2. d=df-di, Sine...
  4. D

    How Does River Flow Affect a Swimmer's Resultant Velocity?

    1.A girl can swim 4.5m/s. If she tries to swim across a river flowing at 3.8m/s, what is her resultant velocity? 2. cosine, sine, tangent, v=vf -v i 3. would i just subtract 3.8m/s from 4.5m/s in order to find the velocity?
  5. P

    Relative Motion: Solving for Time Elapsed for Boats A & B

    Homework Statement The raceboats A and B leave at the same time the beach at point O with zero initial velocity. The path of boat A forms an angle of 60º with the beach and the path of boat B forms an angle of 45º. Both boats move with constant acceleration. Compute the time elapsed until the...
  6. J

    Relative Motion using Rotatin Axis

    Homework Statement While the bridge is closing with a constant rotation of .5 rad/s, a man runs along the roadway such that when d=10ft, he is running outward from the center at 5 ft/s with an acceleration of 2 ft/s^2, both measured relative to the roadway. Determine his velocity and...
  7. K

    Relative motion of C on C formula

    I need to prove the affect of relative motion on C if the velocity is C. The Relativistic Doppler Affect is not accurate correct? I am calculating only direct motion no adjustments for radial velocity etc. needed
  8. K

    Hypothetical Brain Teaser about Relative motion and the finite speed of light

    The essay question I have chosen for my assignment is the following: " If you are traveling in a car at the speed of light and you turn on your headlamps, will the light emitted illuminate the path in front of you?" I am not concerned with the car or its occupants in any...
  9. K

    Relative motion -cheetah and gazelle

    Homework Statement A cheetah can run at approximately 100km/hr and a gazelle at 80km/hr. If both animals are running at full speed, with the gazelle 70m ahead, how long before the cheetah catches its prey? Homework Equations s=vt (no acceleration) v = km/hr / 3.6 = m/s The Attempt at a Solution...
  10. F

    Relative Motion Question Involving Rain and Moving Car

    Homework Statement A car travels due east with a speed of 45.0 km/h. Raindrops are falling at a constant speed vertically with respect to the Earth. The traces of the rain on the side windows of the car make an angle of 45.0° with the vertical. Find the velocity of the rain with respect to the...
  11. L

    Relative Motion Homework: Snow Falling Angle at 6.9 m/s, 79 km/h

    Homework Statement Snow is falling vertically at a constant speed of 6.9 m/s. At what angle from the vertical do the snowflakes appear to be falling as viewed by the driver of a car traveling on a straight, level road with a speed of 79 km/h? _________ degrees Homework Equations...
  12. S

    Why should A change its view on the length of B ship during relative motion?

    Two MM-devices A and B (=two perpendicular arms x and y being the paths for light signals) are at rest in the same frame. Both arms are of equal length, say, 1 light-second long. B is accelerated away along the positive x-axis and reaches relative velocity, say, 0.5 c. I asked: will B have to...
  13. C

    Relative Motion in 2D - a plane & wind speed.

    Homework Statement A plane attains an airspeed of 620 km/hr. The plane sets out for a destination 1085 km to the north (a 0° course) but discovers that the plane must be headed 20° east of north to fly there directly. The plane arrives in 2.00 h. What is the wind speed? What is the direction...
  14. K

    Relative Motion - River/Boat problem

    Homework Statement A boat takes 2.80 hours to travel 30.0 km down a river, then 4.50 hours to return. How fast is the river flowing Homework Equations Vac = Vab + Vbc The Attempt at a Solution I wasn't quite sure how to use the formula that the professor gave us which is above for...
  15. N

    Friction and relative motion 2

    Homework Statement A sled weighing 60 N is pulled horizontally across snow so that the coefficient of kinetic friction between sled and snow is uk = 0.100. A penguin of 70 N rides on the sled. If the co. static friction between the penguin and the sled is us = 0.700 find the maximum...
  16. N

    How Long Does It Take for a Block to Slide Across Another with Applied Force?

    Homework Statement A block of mass m rests on the left edge of a block of length L and mass M. Coefficient of kinetic friction between m and M is u. There is no friction between the bottom block (M) and the floor. A constant horizontal force F is applied to mass m, setting it in motion. How...
  17. O

    Solving for The Relative Motion of a Boat: Angle & Speed

    Homework Statement suppose the boat is initially at x = 0, y = 0. and the dock is located at x = 55 m, y = 11.7 m relative to this starting point. Assume that the speed of the boat relative to the water is 5.0 m/s and that the speed of the water relative to the ground is 1.4 m/s. (a) At what...
  18. J

    Relative motion involving vectors(kinematics)

    Homework Statement Ship A is located 3.5 km north and 2.8 km east of ship B. Ship A has a velocity of 22 km/h toward the south and ship B has a velocity of 40 km/h in a direction 37° north of east. At what time is the separation between the ships least? Homework Equations...
  19. J

    How Do Ships A and B Move Relative to Each Other?

    Homework Statement Two ships, A and B, leave port at the same time. Ship A travels northwest at 22 knots and ship B travels at 29 knots in a direction 40° west of south. (a) What is the magnitude the velocity of ship A relative to B? (b) What is the direction of the velocity of ship A...
  20. F

    How Does the Speed and Direction of a Car Affect the Apparent Angle of Rainfall?

    While driving north at 25 m/s during a rainstorm you notice that the rain makes an angle of 38 degree with the vertical. While driving back home moments later at the same speed but in the opposite direction, you see that the rain is falling straight down. From these observations, determine...
  21. W

    Relative Motion Question (PHYSICS 20)

    Homework Statement You swim from the west to the eastern shore across a 30m wide section of the bow river at 3.5m/s @ 30° N of E. If the river flows southward at 4.0m/s, determine your resultant velocity/ Homework Equations - Trig (SOH CAH TOA) The Attempt at a Solution So...
  22. W

    How Does Relative Motion Affect Perceived Velocity?

    If you are an observer standing still, what can you say about the relative velocity of an object moving toward you? If you are moving toward an object that is also moving? Vyg + Vog = Vyo I believe that the answer would simply be that the velocity of the object moving toward you...
  23. W

    Relative Motion of a hockey player

    Mario, a hockey player, is skating due south at a speed of 7.1 m/s relative to the ice. A teammate passes the puck to him. The puck has a speed of 12.9 m/s and is moving in a direction of 20° west of south, relative to the ice. What are the magnitude and direction (relative to due south) of the...
  24. T

    Velocity, and relative motion.

    Homework Statement A man can swim at 2ms-1 ( with neglible acceleration) across a current of 1ms-1. He swims towards a point directly opposite his starting position on the river, 10m wide, and always aims to swim across to this point wherever he is on the river a) find how long it takes for...
  25. H

    How Do You Calculate Relative Velocity Between Two Moving Cars?

    Homework Statement if a car 1 is traveling north at 13m/s and another car (2) is driving 20 degrees north of west at 7.0m/s 1.What is the velocity of car 1 relative to car 2 2.What is the velocity of car 2 relative to car 1? i don't understand how to solve this? could someone help, are the...
  26. S

    Airplane drops a package (relative motion)

    Homework Statement A plane flying at a speed of 275 m/s at an altitude of 3000 m drops a package. The plane doesn't change its direction or speed and there is no wind resistance. a) Where does the package hit the ground relative to the point of release? b) Where does the package hit the...
  27. U

    Calculating Relative Motion Using Time and Distance Equations

    A suspicious-looking man runs as fast as he can along a moving sidewalk from one end to the other, taking 2.50 s. Then security agents appear and the man runs as fast as he can back along the sidewalk to his starting point, taking 8.00 s. What is the ratio of the man's running speed to the...
  28. V

    What is the relative velocity of a person running on a ship to the shore?

    Homework Statement A ship is traveling at 8.0 m/s at an angle of 50 degrees north of east relative to the water. The water moves at 3 m/s due south relative to the shore. a- Determine the velocity of the ship relative to the shore. b- A person running along the deck of the ship moves at 2...
  29. S

    Calculating Relative Motion and Vectors for Moving Cars

    Homework Statement Car A's velocity varies as Va=3t^2i + 3tj Car B's velocity varies as Vb= -4ti + 4t^2j Both car's start at t=0. a) Find the position of Car A with respect to Car B at t=1 second. b) Find the velocity of Car B with respecto Car A at t=2. The Attempt at a Solution...
  30. D

    Relative Motion and Time Dependance on Velocity of Light

    The relative motion and the relative time of any inertial system to another one is in literature available (to me) subject to multiplication by a factor lambda = (1-v^2/c^2)^-1/2. It is found in the Lorentz transformation as well as STR. Is it possible to arrive at the same result and formulae...
  31. R

    Calculating Wind Velocity Using Vectors

    Homework Statement A jetliner with an airspeed of 1000 km/h sets out on a 1500-km flight due south. To maintain a southward direction, however, the plane must be pointed 15 degrees west of south. If the flight takes 100 min, what is the wind velocity? The Attempt at a Solution This one has...
  32. mtworkowski@o

    How does relative motion affect the speed of light?

    I have a problem with relitive motion. If a light source is moving toward me a some high percent of c, the light will not reach me any sooner than if the light were stationary. The intantanious position of the light is the only thing that matters. Light is bound by a maximum propigation rate...
  33. L

    Relative Motion, a confusion

    What two speed measurements do two observers in relative motion always agree on? In my opinion, one will be relative velocity...but can't figure out the other..? Any ideas? Also, photons of light have zero mass. How is it possible that they momentum? Cuz Momentum=mv...so if m is zero...
  34. M

    How Does Jet Stream Speed Affect Airplane Ground Speed?

    Homework Statement Long flights at midlatitudes in the Northern Hemisphere encounter the jet stream, an eastward airflow that can affect a plane's speed relative to Earth's surface. If a pilot maintains a certain speed relative to the air (the plane's airspeed), the speed relative to the...
  35. V

    Archived Relative Motion in Two Dimensions

    Homework Statement A light plane attains an airspeed of 500 km/h. The pilot sets out for a destination 800 km due north but discovers taht the plane must be headed 20.0 degree East of due North to fly there directly. The plane arrives in 2.00 h. what were the (a) magnitude and (b) direction of...
  36. F

    Rami Running at 0 Vel: Solved Relative Motion

    [SOLVED] Relative Motion Homework Statement Rami is running along the walkway so that his velocity relative to the ground is zero? How fast and in what direction is he running? Homework Equations V(a,b)= V(a) - V(b) The Attempt at a Solution V= 0- V(b) I am not really a sure...
  37. T

    What is the solution to this relative motion problem?

    Homework Statement http://img221.imageshack.us/img221/5571/kinematicslz1.jpg I asked my teacher to clarify this question a bit more, and she said that the man wanted to end up exactly opposite to where he was on the west shore, or in other words, parallel to where he was from the east shore...
  38. W

    Calculating Relative Motion of A, B, & C: Agree?

    This is indirectly addressed in some posts but I can't find a direct answer to the following: consider moving frames A, B, and C (e.g., A, B, and C are 3 trains moving at different speeds on the same track; or A is a train, B is a person walking inside the train holding a tray, and C is a...
  39. O

    Special Relativity and Relative motion

    1. Homework Statement An observer on Earth sees two spaceships moving in opposite directions and finally they collide. At t=0 the observer on Earth says that the spaceship 1 which moves to the right with Ua=0.8c is at the point A and the spaceship 2 which moves to the left with Ub=0.6c is at...
  40. O

    Relative Motion: Collision of Two Spaceships on Earth

    Homework Statement An observer on Earth sees two spaceships moving in opposite directions and finally they collide. At t=0 the observer on Earth says that the spaceship 1 which moves to the right with Ua=0.8c is at the point A and the spaceship 2 which moves to the left with Ub=0.6c is at...
  41. R

    How Do Wind and Plane Speeds Combine to Affect Ground Velocity?

    Hi, I am having troubles with a question concerning relative motion. The problem goes: A plane is traveling at an air speed of 285 km/h [E45ºS]. A wind is blowing to the northeast at 75 km/h [N22ºE] relative to the ground. Determine the velocity relative to the ground. My teach prefers...
  42. P

    Can Uniform Relative Motion Turn a Wormhole into a Time Tunnel?

    Consider a wormhole. Suppose its two mouths have no relative motion with each other. Therefore no time difference exists across its ends. It provides a mean to travel faster than "light in normal space". Imagine this wormhole to be at rest in frame "S" (say). If there is another...
  43. K

    Projectile Motion and Relative Motion Principles

    Homework Statement A baseball player is running with the ball and throws it to first base in an attempt to get the runner out. Describe the considerations the player must take into account in order to be successful. Include the concepts of projectile motion and relative motion principles...
  44. I

    Good video about relative motion

    a baseball is fired out of the back of a truck going 60mph at 60mph
  45. K

    Relative motion of a light plane

    Homework Statement A light plane attains an airspeed of 470 km/h. The pilot sets out for a destination 840 km due north but discovers that the plane must be headed 24.0° east of due north to fly there directly. The plane arrives in 2.00 h. What were the (a) magnitude and (b) direction of the...
  46. K

    Relative motion in three dimensions

    A light plane attains an airspeed of 470 km/h. The pilot sets out for a destination 840 km due north but discovers that the plane must be headed 24.0° east of due north to fly there directly. The plane arrives in 2.00 h. What were the (a) magnitude and (b) direction of the wind velocity? Give...
  47. Amith2006

    Change in area due to relative motion

    Homework Statement 1) A square of area 100 cm^2 is at rest in the reference frame of O. Observer O’ moves relative to O at 0.8c along the diagonal of the square. What is the area measured by O’? Homework Equations The Attempt at a Solution I solved it the following way: I...
  48. A

    Relative Motion (Swimmer Crossing River Question)

    Homework Statement A swimmer who can swim at a speed of 0.80m/s in still water heads directly across a river 86m wide. The swimmer lands at a position on the far bank 54 m downstream from the starting point. Determine: (C) The direction of departure that would have taken the swimmer...
  49. W

    Problem with understanding of relative motion.

    Hi everyone, I have a problem with understanding a few lines from the book on Relativity I am using. Let me first quote my troubles, "Let us express these facts algebraically, for two observers, K and K', who are moving with uniform velocity relatively to each other, thus: K writes x = ct...
  50. P

    How Fast is the River Flowing in the Fisherman's Problem?

    Problem: A fisherman sets out upstream from Metaline Falls on the Pend Oreille River in northwestern Washington State. His small boat, powered by an outboard motor, travels at a constant speed v in still water. The water flows at a lower constant speed vw. He has traveled upstream for 2.00...
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