Velocity Definition and 1000 Threads

The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of an object's speed and direction of motion (e.g. 60 km/h to the north). Velocity is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of bodies.
Velocity is a physical vector quantity; both magnitude and direction are needed to define it. The scalar absolute value (magnitude) of velocity is called speed, being a coherent derived unit whose quantity is measured in the SI (metric system) as metres per second (m/s or m⋅s−1). For example, "5 metres per second" is a scalar, whereas "5 metres per second east" is a vector. If there is a change in speed, direction or both, then the object has a changing velocity and is said to be undergoing an acceleration.

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  1. M

    Calculate the Angular Velocity of an Arm from a Data Set

    Hi, a newbie to the site and hoping someone can help. Its been a long time since I studied physics or math at school. I am having some difficulty calculating the angular velocity of the arm trhough a partial movement (phase). The data set I have separates the angular velocity into the three...
  2. M

    Velocity of COM after collision

    I calculated that the velocity of the head prior to the collision is sqrt(2gh), as all of the gravitational potential energy is converted to kinetic energy. And I believe the velocity at point A after the collision is given by the formula vf=e•sqrt(2gh), with e representing the coefficient of...
  3. K

    Coefficient of friction for constant velocity given a constant force

    ...
  4. J

    Equating two formulas for root-mean-square velocity

    (a) My question : Are all the formulas correct? If so I can write ##v_{rms}## in form (2) and compare that result with the other velocities to get the answer (rms > average > most probable)
  5. T

    Velocity of a slider immediately before impact

    T1 + V1 = T2 + V2 0 + mAgh = 0.5mAV2A1 + 0 40 = (5/32.2)VA2 VA1 = 16.0499 ft/s Edit: Accidentally Used two notations for Kinetic Energy in the "Useful equations" section. Changed it to correctly notate Kinetic and Potential. This notation is used in R.C. Hibbeler Dynamics 14th Ed.
  6. D

    MHB Angular Velocity - 2100 Revs in 3 Mins - 73.3 Rad/s

    (i) A rotating machine shaft turns through 2100 revolutions in 3 minutes. Determine the average angular velocity, w, of the machine shaft in rad/s. the answer for this is 2100 x 2 pie = 4200 pie radian 3 mins = 180 seconds 4200 / 180 = 73.3 rad/s (ii) Determine the area and arc length of the...
  7. J

    Unable to clearly understand relative velocity

    Unable to understand why this is the case? Also, if it were in two dimensions then I am guessing the same would apply, only the 'x-co-ordinates' and 'y-coordinates' would add up separately? Lastly, does the same hold for acceleration. I am aware that this is a trivial question, many books...
  8. R

    Center of Mass of acceleration and velocity

    I don't understand what I am supposed to do. I know how to find the acceleration of the system, but I am not sure how to find the com acceleration. My guess would be something along the lines of xcom = (m1a1*x + m2a2*x)/(m1a1 +m2a2). Then do the same for the y axis. Then to find the velocity all...
  9. E

    Circular Motion Question: Change in Vector Angular Velocity

    Hi i am e-pie's brother and he let me use his account.Since $$\vec{\omega}$$ is always perpendicular to the plane.Shouldn't this be $$0^o$$?
  10. M

    How to find the velocity of a wave in simple harmonic motion given time

    The graph provided is below. The problem asks for the speed of the wave at 0.12s. I used the formula v=w*xmax*cos(wt), provided in our textbook where xmax is the amplitude of 2 cm, w (omega) is 2pi divided by the period of 0.2. However, for some reason this formula doesn't give me the correct...
  11. T

    Sonic velocity inside a convergent nozzle

    This time, i have a question that came to my mind a few days ago. There is an ideal nozzle having inlet to throat ratio of 8:1. Air will enter the nozzle at around 84 m/s velocity. it can be easily understood that the velocity will become sonic much ahead of the throat. And I am wondering what...
  12. H

    MHB Velocity Time graphs: Find acceleration in the first 15 mins in km/h^2

    Helpp meee pleaseee
  13. K

    Hard time with this Vector Velocity Problem

    Summary: I've posted this in a few forums but still confused on this problem. If the plane is moving at 200km/h and the wind pushes the plane with a velocity of 85km/h, then the resultant velocity would be 217km/h, and using sine inverse, 217.sin(theta=85, I got 23°, which is B, but the answer...
  14. O

    Dynamics Problem: Determine Velocity and Acceleration of Rigid body

    Hello, Wanted to know if this was the correct approach to solve this example. I uploaded the question along with an attempt. Thanks in advance.
  15. lilymay992

    What is the maximum speed of a proton if its kinetic energy is 1.28x10^-14 J?

    So first I tried to use KE=1/2 x m x v^2 but then realized I didn’t have the velocity and I can’t figure out a way to obtain it. I then tried to work out the energy using a different equation, W= q x v but that left me with 1.28x10^-14 J which seemed too small. I also then have to calculate the...
  16. pluralangel

    seeking help finding the initial velocity of a type 3 projectile

    hi, so I've been trying to find the initial velocity of this projectile; but i ended up getting a negative value for seconds squared. I've gone over my solution multiple times but don't see where i went wrong. alternatively, was i supposed to take the absolute value of seconds squared? thanks...
  17. rexxii

    Velocity required between two connecting shafts

    Summary: Constant Velocity between two connecting shafts? Many mechanical machines have a requirement for two shafts to be joined. Explain the requirements for constant velocity ratio between the two shafts? I think this is to do with the requirement for continual acceleration and direction...
  18. G

    How does the release angle of a catapult affect the object's velocity?

    [Moderator: repeated text removed.]
  19. N

    How to calculate change of velocity after hitting water?

    Me and a Partner are presenting the physics of diving as our final in physics. He wants a ton of detail about the activity we choose so I thought it would be a good idea to show the difference from a cannonball vs a normal dive and the change in velocity that occurs with both, and also how much...
  20. I

    Where does the equation of the velocity of a free vortex come from?

    I am aware of the equation of the velocity of a forced vortex, which is simply ## v = r\omega ##. However, the velocity for a free vortex is ## v = \frac{c}{r} ## (## c ## is the 'circulation constant', ## r ## is the radius, ## v ## is the velocity and ## \omega ## is the angular velocity). I...
  21. vsarnaud

    4 Linkage system: velocity calculation

    For the attempt at a solution view the Excel screenshots (1). A screenshot with all the lengths is provided (2). The 4-linkage system is shown in screenshot (3). The problem is shown in screenshot (4). A screenshot from the whole assembly is also provided to add some insights (5). Thanks...
  22. olgerm

    The derivative of velocity with respect to a coordinate

    Why ##\frac{\partial (0.5*m*\dot{x}^2-m*g*x)}{\partial x}=-mg##? why ##\frac{\partial \dot{x}}{\partial x}=0##? Why ##\frac{\partial (0.5*m*\dot{x}^2-m*g*x)}{\partial \dot{x}}=m*\dot{x}## ? why ##\frac{\partial x}{\partial \dot{x}}=0##? Does it assume that speed is same at every location? I...
  23. S

    Is the Velocity Calculation Affected by Gravity or Elastic Potential Energy?

    Hi all! I was attempting the following question but my answer differed from the given answer. Please help me to solve it. Thanks. My answer = 2.45 m/s Given answer = 3 m/s
  24. James Beedy

    How to Calculate the Recessional Velocity of a Galaxy 500 Mpc Away?

    I need to calculate the recessional velocity of a galaxy 500 Mpc away. I need to express my answer in KM, distance in speed, age of the universe in seconds and years.
  25. emarie

    Calculate the magnitude of the velocity at point from a given equation, a(t)

    These questions keep appearing in my past-papers and yet at no point in the course notes can I find a worked solution. Unfortunately I'm not sure where to start. My initial thoughts were regarding getting an equation using known values but w.r.t. to t and integrating for v, but like I said I...
  26. D

    How to find the velocity of a water leak in a spinning tank

    We have a cylindrical water tank that spins over its axis of symmetry with constant angular velocity ω. Here's a diagram: We wish to find: 1 - The tangential and radial components of the velocity of the water as it leaves the tank. 2 - The radius r reached by the water. I'm not sure at all...
  27. P

    Finding the change in velocity through a potential difference

    We're given the equation qB=mv/r which is simple enough. I just don't know how to find the velocity given the acceleration through a potential difference. I tried using the radial acceleration equation given to me but I end up with the square root of a negative...and that breaks math... I...
  28. T

    Relative Velocity of Swimmer: How to Calculate Total Time for Different Paths?

    So I was just wondering if someone could check my method for (b) as sometimes I can have a tendency of getting the relative components wrong ect. Diagram 1 (a) Time for PY: ##T=L/c## Time for YP: ##T=L/c## Total Time:##2L/c## (b) Velocity for PY: ##c-v##...
  29. F

    Orbital velocity of a craft at 4km above the Moon's surface

    What would be the orbital velocity of craft at 4km above moon surface? Assume a mass of 1,000,000 lb, US.
  30. B

    Relative velocity between a Bus and a Car

    for part 1: t= d/s = 9000/13 = 692.31s for part 2: What i am unsure about is wether or not this is after the initial observation or exactly what they are asking honestly. so i found the relative velocity of the bus to the car and vice vera and came up with: t=d/s = 9000/4 = 2250s however i don't...
  31. K

    Velocity of a charged particle

    Hi. I will be glad if you can help me with a small problem. I got a cylinder with a density $$ \rho (r) = b \cdot e^{\lambda r} $$, with radius $$ R $$. If I let go a charge q < 0 from $$ R_0 $$ when $$ R_0 > R $$ , what will be the velocity that the charge will hit the axis of the cylinder.So...
  32. Josh chips

    Find the initial velocity of the second stone

    since the question states they hit the ground at the same time i firs find the time they hit the ground y= ut + 1/2at^2 initial velocity is 0 for the first stone 320= 0 + 4.9t^2 this t= 8 secs since the 2nd stone was thrown 100 m below stone 1 distance from ground is 220m 220 = ut -...
  33. H

    Chain problem - velocity as the chain becomes completely vertical

    To start this problem, I used equation (1) K_i + U_i = K_f + U_f Then, using (2) and (3) and knowing that the initial velocity is 0, I have m_igy_i = \frac{1}{2} m_fv_f^2 + m_fgy_f The mass of the hanging part of the rope is ## \frac{y_0}{L} m ##. Additionally, I set the face of the table...
  34. R

    Relative velocity between lift and screw

    v=16m/s+4*.659s=18.636m/s (for lift) v0=16m/s-9.81*.659s=9.53m/s my question is that why 16m/s is considered for screw velocity ? it is given for lift .what does it mean 9.53m/s? If you drop something , it gets acceleration and I calculate it 6.45m for screw while falling and why should I...
  35. Warbow

    Arrow passing through a moving target -- What is the final velocity?

    A 0.1 kg arrow is moving at 48 m/s to the right and strike a 3 kg object (helmet resting on a 5 kg head) moving to the left towards the arrow at 9 m/s (full mounted charge). It takes 80 Joules to penetrate the 3 kg helmet, what is the velocity of the arrow after penetration when it slams into...
  36. Y

    Is the propagation velocity slow down at low audio frequency?

    I uploaded the paper from Belden cable company. It said the velocity slows down to 5EE6 m/sec from 1EE8 m/sec at RF speed. I don't remember I ever read this before, I thought velocity = 1/sqrt( μ/ε). Please give me a link on the reason if this is true. Thanks Alan
  37. C

    What are some common misunderstandings about magnetism and relativity?

    Hello, there are a couple things about magnetism that I do not understand. 1. Why didn't we define the magnetic field to be in the directions of the force? This isn't really a technical question, I am just more curious about why it is this way. The way I was thinking of it, the math seems to...
  38. zehkari

    Find the position of a proton in an E and B field

    Hello all, I have a question with the helix path of proton in a magnetic field that I am a bit stuck on. Question: Equations: F = qv X B F = mv^2/r d=vt My Attempt: Think the graph drawn is good enough for questions (a). However, I am stuck on (b) and (c). Firstly I am not entirely sure...
  39. S

    What is the maximum velocity of a bullet at the instant it leaves the barrel?

    hi, my high school physics is letting me down here and I just have to get an explanation... when you talk to gun guys, they say that the maximum velocity that a bullet reaches is the muzzle velocity ... i.e. the absolute velocity of the bullet at the instant that it clears the...
  40. T

    How to find initial velocity with only an angle and distance?

    I am in Algebra 2 and the homework asks a question: "You and a friend arw driving golf balls at a driving range. If the angle of elevation is 30 degrees and the ball travels 625 feet horizontally, what is the initial velocity of the ball?"
  41. A

    Velocity gradient decomposition of a fluid flow

    If the velocity gradient decomposition is done by symmetric and antisymmetric parts then ##\frac{\partial v^i}{\partial x^j}=\sigma_{ij}+\omega_{ij}## where ##\sigma _{ij}=\frac{1}{2}(\frac{\partial v^i}{\partial x^j}+\frac{\partial v^j}{\partial x^i})## and...
  42. C

    Express torque as a function of angular velocity

    I am strugglin with this step in my assignment. I am dealing with a centrifuge with a known moment of inertia. I should write the expression for a torque of the motor and express it as a function of angular velocity. Can you help me please?
  43. M

    Finding the change in velocity from an acceleration vs time graph

    Homework Statement The graph shows the variation with time t of the acceleration a of an object (graph attached). What is the change in velocity of the object in the time interval 0 to 4s? Homework Equations a = v/t The Attempt at a Solution My initial answer was -8 m/s, by simply finding the...
  44. EEristavi

    Motion in 2 Dimensions & Relative velocity

    Homework Statement The water in a river flows uniformly at a constant speed of 2.50 m/s between parallel banks 80.0 m apart. You are to deliver a package across the river, but you can swim only at 1.50 m/s. (c) If you choose to minimize the distance downstream that the river carries you, in...
  45. F

    Blood flow velocity via Doppler effect

    Homework Statement A Doppler flow meter is used to measure the speed of red blood cells. The frequency of the apparatus is f = 12 MHz. The sensor in the apparatus measure 1.8 kHz beats between the emitted frequency and the frequency of the ultrasound reflected back by the blood cells. The speed...
  46. J

    Finding recoil velocity of an object during a collision

    Hello. I recently began this problem, but the site I'm working this problem on isn't showing me whether the answer is correct or not. Can someone please check my work and just verify that it's correct or state if it isn't and why? 1. Homework Statement A cosmic-ray photon (with mass m...
  47. MedEx

    Find the Velocity given Magnetic field and Magnetic Force

    Homework Statement A proton moves through a uniform magnetic field given by B=(13.7i−22.9j+23.5k) mT. at time t1 v=(vxi +vyj+1.68k)km/s and the magnetic force is given by F= (4.22e-17i + 2.52e-17j). What are vx and vy Homework Equations F=q(v x B) The Attempt at a Solution First I converted...
  48. Yasin

    Maximum Angular Velocity of a quarter circle

    Homework Statement Finding the general formula for max angular velocity ( answers say 0.839*(g/b)) but I do not understand how Homework Equations 0.839*(g/b) The Attempt at a Solution
  49. Z

    When would a rocket return that was at escape velocity

    we all know escape velocity is a velocity in which a body can escape orbit around the Earth and fly off into space. this needs to happen in space our just out of our atmosphere, due to drag that could bring an object back into orbit and cause it's velocity to degrade to a point where it would...
  50. DeathByKugelBlitz

    Kinetic energy and velocity of electron after compton scatte

    Homework Statement A photon with an initial wavelength of 0.1120 nm collides with a free electron that is initially at rest. After the collision the wavelength is 0.1140 nm . a) What is the kinetic energy of the electron after the collision? b) What is its speed? c) If the electron is...
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