# 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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28. ### B Time Dilation & Relative Motion: Who Measures Proper Time?

Consider the example of flashing light in spaceship. The observer in the spaceshipe and the observer in the Earth measure different times. Both observers could argue that the clock of the other tick slower(motion is relative). But is anyone right ? I mean the one will measure proper time...
29. ### Relative Motion of Charges Question

This problem seems pretty simple but I don't understand how the correct answer is 500,000 smaller than what I calculated. You have an electric field that has a magnitude of 10^6 V/m in the positive z direction. I assumed (though it was not stated) that the cause of this field was a sheet of...
30. ### Magnetic Field and a Charged Particle -- relative motion question

Here's a experiment. There is a magnetic field vertically downward and a charged particle is kept inside it. Simple. Does it experience a force? Now if we move a speed of 2m/s relative to the frame of rest charged particle. Then it must experience a force right?(Becuz now its velocity is not...
31. ### Determine the ground speed and the course of the plane

Homework Statement 15.1 The airspeed of the plane is 200m/s, directed north. If the wind speed is 30m/s in the direction shown, determine the ground speed and the course (angle θ) of the plane. Homework Equations The Attempt at a Solution Is it so far correct the above? More questions...
32. ### Problem using vectors and relative motion

Homework Statement A river of width 4 km flows at 5 km/h. A swimmer whose speed relative to water is 4 km/h, starts swimming from a point A on a bank. What minimum distance will the swimmer have to walk on the other bank to reach point B directly opposite to A? [/B]Homework Equations Vba = Vb...
33. ### B Relative motion and proper time

Hi everyone! Sorry for the bad english! Quick question Just to see if I understood: If a person on a spaceship moving at 0.7c in relation to a person in the earth, and both of then agreed they started making microwave popcorn at the same time (like when the spaceship is just above the head of...
34. ### B Why Does Vqp Need to be Tangential to Vq in Order for Q to Get Closest to P?

https://www.physicsforums.com/attachments/221718 Say if we have two particles P, and Q, traveling at velocities Vp and Vq respectively. If it is IMPOSSIBLE for Q to collide with P, let us find the distance of closest approach. So from the frame of reference of P, itself is stationary, and Q is...
35. ### What Is the Speed of the Man Relative to the Ground?

Homework Statement If a river is going 6 km/hr relative to the ground, a boat is going 14 km/hr relative to the river, and a man is jumping from one end of the boat to the other at 6 km/hr relative to the river. What is the speed of the man relative to the ground? I'm stuck between the...
36. ### Kinematics -- flying a plane in the wind to a destination

Homework Statement A plane is taking off from an airport directly west of the airport it wishes to touch down in. The plane in still air can travel with a constant speed of 730 km/h. If a wind is blowing constantly at 92 km/h [45° S of E], at what angle must the plane fly to compensate for the...
37. ### Relative motion of converging objects

If two objects are traveling on paths at 90 deg to each other such that they will converge at a point how do we describe that motion. For example 2 cars are approaching a 4 way intersection and will collide. They see each other as moving diagonally yet when they collide one will t-bone the...
38. ### B Synchronize Clocks in Relative Motion: How & Why

Is there any way to synchronize two clocks already in relative inertial motion? If so, how? And I am not sure exactly what “synchronize” would mean in that context. Maybe it would mean that their readings, or at least their running rates, would match when their relative motion was stopped? There...
39. M

### What is the angle and displacement of the plane?

Homework Statement In the figure below, a radar station detects an airplane approaching directly from the east. At first observation, the range to the plane is d1 = 412 m at 40° above the horizon. The airplane is tracked for another 123° in the vertical east–west plane, the range at final...
40. ### Voltage due to relative motion of a charge and conductive loop

Consider an electric charge Q with rest frame R and a closed conductive loop L with rest frame R'. Q is moving relative to L, and vice versa. In R, the loop is moving and receives no magnetic flux from Q thus no voltage according the integral form of Faraday's law. In R', the loop receives...
41. ### Relative motion of two observers

Homework Statement Two observers having identical instruments carry out identical experiments to study the motion of a massive particle. First observer concludes that the particle is moving in a straight line with constant velocity while the second observer concludes that the particle is moving...
42. ### I Relative Motion vs Time: Paradox Explained

Hi, I'm reading a book explaining relativity. I previously understood the subject in layman's terms but am now confused. The author has introduced relative motion in an invariant universe with the concept that motion through space is only relative to the observer. Given this, I'm now...
43. ### Relative motion problem with airplane and wind velocity

Homework Statement A small airplane wants to fly from A to B which is 200 km due south. The wind is blowing towards the east at a velocity of 50 km/h. If the airplane can move through the air at 300 km/h, find the direction the plane should be heading; the speed of the airplane relative to the...
44. ### Derivation of Rocket Equation Using Relative Velocity

Based on my current understanding of the problem I do not see this following derivation as valid, although this is what was given in my course notes. Although this particular example is from an undergraduate physics course this is not a homework problem: I'm confused about the underlying...
45. ### What is the Correct Direction of Hay Bales in a Basic Relative Motion Problem?

Homework Statement A farmer is throwing bales of hay off the back of his tractor with a speed of 3 m/s relative to the tractor, which is moving west with a speed of 7 m/s. Determine the speed and direction of hay bales relative to the ground. Homework Equations subtract the speeds, since they...
46. ### Relative Motion: Calculating the Angle for Accurate Newspaper Delivery

Homework Statement Homework Statement A newspaper boy throws papers sideways onto the porches of his customers while riding his bicycle along the sidewalk. The sidewalk is 15m in front of the porches. The boy throws the papers at a horizontal speed of 6m/s relative to himself, and rides the...
47. ### How Fast is the Airplane Flying Relative to the Air?

Homework Statement After flying for 15 min in a wind blowing 42 km/h at an angle of 31° south of east, an airplane pilot is over a town that is 50 km due north of the starting point. What is the speed of the airplane relative to the air? Homework Equations Vx of wind=42km/hr*cos(31) Vy of...
48. ### Understanding Relative Motion in Circular Motion

Homework Statement Homework Equations a= omega^2*r The Attempt at a Solution a_A/B = a_A - a_B a_A = 10^2*r (-î) a_B = 10^2*r (+ĵ) a_A/B = 10^2*r (-î) - 10^2*r (+ĵ) => -200 î -200 ĵ why is the answer 200 î -200 ĵ (accelerate in +î direction) ?
49. ### Calculating Sailboat Relative Motion with Equations and Conversions

Homework Statement Homework Equations v_theta = r * theta_dot 1 knot = 1852 m The Attempt at a Solution v_0 = 6 * (1852m/h) * (1/3600 h/s) = 3.087 m/s
50. ### Minimum distance between bomb and shell

1. Prolem Statement:- An aircraft is flying horizontally with constant velocity = ##200 m/s##, at a height = ##1 km## above the ground. At the moment shown, a bomb is released from aircraft and the canon- gun below fires a shell with initial speed = ##200 m/s##, at some angle #\theta#. 1)For...