# Velocity Definition and 525 Discussions

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. ### Determine vertical velocity vector on sloped surface

A golf is launched at a speed v,f and launch angle, β,f. The slope of the green is equal to φ. At some point the ball is located on the rim of a hole. The side view (a) and overhead view (b) looks as in the attached image. According to the author of the [paper] "The Physics of Putting" the...
2. ### Momentum Collision Homework Problem -- help please

Parallel: M1V1+M2v2=M1V1’+M2V2’ (0.5)(3)+0=(0.5)(cos60)(3)+V2’Cos(x)(0.5) V2’cos(x)= Perpendicular: M1V1+M2v2=M1V1’+M2V2’ 0=(0.5)(0.3)(sin60)+V2’sin(x)(0.5) V2’sin(x)= And the divide 2 by 1 Which is tan(x)=2/1 And then plug then back in to solve, but I don’t think we do it like this because...
3. ### Ball rolling down a slope problem: Find an expression for time taken

Question: Galileo released a metal ball from rest so that it could roll down a smooth inclined plane. The time t taken to roll a distance s was measured. He repeated the experiment, each time recording the time taken to travel a different fraction of the distance s. Write an expression for the...
4. ### A small diamond of mass 10.0 g drops from a swimmer’s earring and falls through the water

b) My question is here! 0.9v_t = v0 + a*t = a*t t = 0.9v_t/a delta_h = v0*t + 0.5*a*t^2 = 0.5*a*t^2 = 0.5*((0.9*v_t)^2)/a = where a = (-m*g + b*v)/m delta_h = (0.5*((0.9*v_t)^2)*m)/(-m*g + b*v) plugging in everything delta_h = 1.65 m which is not what the answer is. Please help
5. ### Making a Velocity vs Time graph for a bullet

Here is my working in case it helps :)Ignore the v = 0.6/0.0001 = 6000m/s
6. ### Finding the angle and velocity at which a space station reaches the moon of the planet

A station is orbiting a planet at a distance R1, a moon is orbiting the planet at distance R2 with the period T. The planet itself has a radius rp and a mass mp. We know that when an object adds its velocity at a point in the orbit, the height of the opposite orbit will increase. Determine the...
7. ### Finding the acceleration of the ball in contact with the ground during bouncing

the v before hitting the ground immediately=4.85m/s the v after hitting the ground immediately= 3.96m/s I considered the down positive, then v= u+at 3.96= 4.85+ (a*0.16) so a= -5.56m/s*s The answer is 55m/s*s The parts that I don't get are why it must be -3.96 and why that velocity becomes...

9. ### Find the equation of this magnetic field

When I try following numbers from internet then I don't get an expected answer. ## \mu_0 = 1.25663706 × 10-6 m kg s^{-2} A^{-2}## ##q =1.60217662 × 10^{-19} coulombs ## ##r=2.82x10^{-15} m## Velocity of that electron is given in question ##\vec v= 2 \times 10^6 \\ \mathrm{ms^{-1}}## Since...
10. ### Find second object's velocity in relativity

> A particle of mass M at rest decays into two particles of masses m1 and m2 travelling in opposite directions at velocity v1 and v2 respectively. Express v2 in terms of v1, m1, m2, and M. Since both objects are from a single object that's why I took relativistic mass of both objects are same...
11. ### B Speed/velocity as a derivative

[Note: Link to the quote below has been pasted in by the Mentors -- please always provide attribution when quoting another source] https://www.feynmanlectures.caltech.edu/I_08.html Let s=16t^2 and we want to find speed at 5 sec. s = 16(5.001)2 = 16(25.010001) = 400.160016 ft. In the last...
12. ### Calculating the velocity of a head-on impact between two suns

Firstly I would like to start with solving the problem with energy conservation principle which most solutions to the question show. -Gmm/r= 1/2 mv^2 +1/2mv^2 -Gmm/2R Where m= mass of planet r= initial seperation v= final velocity. R=...
13. ### Acceleration-Time Graph and Velocity Multiple Choice Question

The variation with time t of the acceleration a of an object is shown What is the change in velocity of the object from ##t=0## to ##t=6##? A. ##6ms^{-1}## B. ##8ms^{-1}## C. ##10ms^{-1}## D. ##14ms^{-1}## So apparently the answer is B, which I am having trouble reconciling. Using methods...
14. ### Is there a forum for NYC physics standards K-12?

I am a new tutor working with students in 11th grade physics in New York City. I am required to keep notes internally on the sessions and the standards that I cover in them; after noticing that the physical science standards don’t include mentions of velocity or displacement as a content area, I...
15. ### Intro Physics homework help - distance and velocity

I have tried this problem over 4 times and keep getting the exact same answer, which is incorrect. Could someone please help by pointing out what I did wrong, or letting me know if I am actually on the completely wrong path? Thanks! Have a wonderful day :)
16. ### Finding The magnitude of the velocity

i have tried V=Vi - (g*t) with an answer equals to 4 as well as d=Vi(t) + 1/2 a t^2 with an answer equals to 19 my final asnwer was 1.43 and it was still wrong i used formula a=v/t v=14 t=10 i divided 14/10 to get 1.4
17. ### I Is acceleration a more absolute/fundamental quantity in the universe?

Was wondering if acceleration seems to be a more fundamental property/quantity in the universe as compared to velocity or distance because acceleration can be defined in more absolute terms in a frame depending on the forces acting inside that reference frame. Considering a very simple example...
18. ### Propagation Wave Expressions and Wave Velocity

Hello everyone, I would really appreciate some help on the following problem on plane waves and propagation. Not too sure if my attempt at writing the propagation wave expressions are correct, and how to handle the arbitrary function f(u). For the velocity, the wavelength is not specified, so is...
19. ### B Trying to understand this paragraph on speed, acceleration and velocity from my textbook

I am not able to understand the following paragraph from my Physics textbook;
20. ### Hurricane forces — Comparing the force from a 60 mph wind to a 120 mph wind

The marker wrote that the answer is 4 and it's because m and v double. I don't understand how m doubles??
21. ### Lagrangian mechanics - rotating rod

Hello, It might sound silly, but when I try to calculate the kinetic energy of a rotating rod to form the Langrangian (and in general), why it has both translational and rotational kinetic energy? Is it because when I consider the moment of Inertia about the centre I need to include the...
22. ### 2 Carts on a Track Compressed by a Spring -- What are their Velocities?

a)What is the total energy in the system? Only energy acting on the system assuming the track is level and there is no potential energy of the carts, is the potential energy of the spring. Comes out to 7.8125 using the potential energy of a spring equation. b) What are their velocities if the...
23. ### Determine time after which 4 persons meet in given scenario

The point of confusion is deciding the direction each persons sets out in i.e. velocity direction of each person. Knowing this will probably help in getting the solution. At t=0, I can say that velocity of each person is as shown in diagram below.
24. ### Velocity of an Object given its position as a function of time

Attached is the problem and my work through the problem. I got the problem correct, but my teacher said this could be done quicker on a calculator. Any idea how it could be done quicker.
25. ### Getting the angular velocity using the angular acceleration graph

The answer here is A What i did is getting the area as follows, 2×4×1/2 +3×-6×1/2 +4×-6 = -29 and then use this Δω=ωf-ωi -29=ωf-5 ωf=24 but there is no such choice.
26. ### Slip Conditions for flow between Parallel Plates

The problem states: Two parallel plates separated by distance h, the plate at the top moves with velocity V, while the one at the bottom remains stationary. My initial approach was: I considered, ##du/dy = V/h## and for the shear stress ##\tau = \mu \frac{\partial u}{\partial y}## For...
27. ### 2D asteroid problem

Hi everyone! I don't know how to solve the next problem, and if anyone could explain to me step by step how it is solved I would thank you a lot. I know it's not hard, but I'm not seeing how to do it. Thank you in advance!
28. ### Using Orbital Energy to Calculate Velocity

So what I did first was calculate the initial and final potential energies with Epi=-9.433*10^11 m and Epf = -1.503*10^12 m. Then I found change in potential energy, -5.597*10^11 m. Using this I determined the change in kinetic energy, 5.597*10^11. I then added this change to the initial...
29. ### What velocity does the particle need to get to point B?

It was a long time ago I did these kind of problems so I’m a bit rusty. The only thing I can think of is divide it up to two parts one x and one y. In y the acceleration is sin(a)*9.82? Then put that in the equation and solve for t. In x the there is no acceleration so the formula is x=V0*t, I...
30. ### Velocity, barrel length and bore volume

Hello. How does a bullet propell inside a bore? What determine its velocity? I read that a bullet in cal .44 propelled by black powder from a 3” barrel is as powerful as a .25 ACP, however with a longer barrel, the velocity increase significant. With a 8” barrel a .44 black powder bullet is as...
31. ### Pulley angular velocity problem

Further given: - every beam is infinite stiff - pulleys are massless - cables don't stretch, no slip, and frictionless. -Every pulley has a diameter D except pulley Q. Pulley Q has diameter 0.5*D So what I don't understand is how to calculate/determine the velocity at R and S. Can someone help...
32. ### DV Calculation clarification (rocket booster)

When calculating the dV available from a rocket booster, the below calculation is used: (ISP . g) . ln(Mass when full/Mass when empty) Is 'g' always equal to 9.81 in this equation, or do you use the actual gravitational acceleration that the booster will experience, at it's given altitude, to...

34. ### Some Flight Calculations and the Motion of the Earth

A Problem is posed for a flight from Melbourne to Cairns. Using the formula for rotational speed at latitude - 1) The latitude of Melbourne is approx 38 degrees south with a rotation velocity of 820 miles/hr 2) The latitude of Cairns is approx 17 degrees south with a rotation velocity of 994...
35. ### Direction of resulting displacement

I do not understand part b. I know that x180/pi changes the value into a degree, but i do not understand what's going on inside the bracket. And how did the equation calculated the direction?
36. ### Solving for earthquake transit time via Snell's Law

I was told to solve the second equation above for x to get l2 and l2, but that only gets me those in terms of other unknowns. I'm assuming I just need to solve t for my knowns, but I keep getting caught up by my unknowns. i.e., solving for x gives x = (l2*L*v2)/(l1*v1+l2*v2). Please note "l" is...
37. ### Average speed and average velocity

So thing that confusses me, is what is the difference regarding the calculation of speed and velocity? In think I should use the formula I wrote above to find the average velocity, but I don't understand what the formula for average speed will be then. By the way, when using the formula above...
38. ### I Velocity correction´ formula for the rotation of the Earth

Let´s suppose we are observing the sun and measuring some spectral lines. Does the velocity correction´s formula for the Earth include the rotational velocity components of the Sun as well? or rather are we basically measuring both velocity contributes of Earth and of Sun together (receeding...
39. ### Engineering Scaling of units for equations of motions

In the picture, there is a problem where the t is in units of square root(l/g), and V in square root(gl) I am wondering 1. What it means when time is in units other than time? Does it mean that when solving I have to take time/squareroot(l/g) 2. How did they get square root(l/g). Thank you...
40. ### G-force experienced by a jumper, using a DE

We are given that ##v' = \frac{1}{10}v^2 - g##. I tried using implicit differentiation so that ##v'' = \frac{1}{5}vv' = \frac{1}{5}v(\frac{1}{10}v^2-g)## and set this equal to 0. Hence we have 3 critical points, at ##v= 0##, and ##v = \pm \sqrt{10g}##. Calculating ##v''(0)=-120##, we know the...
41. ### Kinematics without rolling or sliding

I initially thought it is v, because the speed shouldn't change when the tape is on top.
42. ### Translational and rotational velocity

For a cylinder rolling down an inclined plane, does the tangential velocity of a point a distance R from the axis of rotation equal the velocity of the center of mass?
43. ### Particle bouncing between walls

I thought it would be a good idea to pretend that the walls are stationary and that each time the particle hits a wall, it gets a velocity addition of the velocity of the wall it’s hitting. Using this I ended up at the formula V = initial velocity of particle + n(velocity of left wall) +...
44. ### Converting Velocity Vector Formula from Cartesian Coordinate System to Polar Coordinate System

I have a little question about converting Velocity formula that is derived as, ##\vec{V}=\frac{d\vec{r}}{dt}=\frac{dx}{dt}\hat{x}+\frac{dy}{dt}\hat{y}+\frac{dz}{dt}\hat{z}## in Cartesian Coordinate Systems ##(x, y, z)##. I want to convert this into Polar Coordinate System ##(r, \theta)##...
45. ### Α baseball player throws the ball...

Hi all ! I wonder if I'm right. (From : Fundamental University Physics, Volume 1 (Mechanics) - (Marcelo Alonso, Edward J.finn) Addison Wesley 1967) This is my try: * I have the Greek version of the book and there is no answer. Thanks.
46. ### Velocity of the center of mass in constrained motion

I tried getting the velocity of a which by using constraint came out to be 3 and by using the eqn for vcom i got the ans as 3.5 i just want to confirm is this the correct answer
47. ### A question of kinematics involving a changing velocity vector

The statement "at the initial moment of time v ⊥ u and the points are separated by a distance l " gives us a picture like the one which I have added in attachment. As the time passes velocity vector v would gradually change from fully vertical to fully horizontal in order to meet point B. Now...
48. ### Doppler Effect Problem

Pretending the siren is at rest in air: Wavelength = velocity/frequence --> (343 m/s) / 10,000 Hz = .0343m. I don't believe this is the correct way to go about solving the problem, since the vehicle is moving at the start and the siren is not at rest.

50. ### MATLAB Spring mass impact system in Matlab - How to correct it?

I am new to Simulink and I wanted to start practicing using a spring mass damper system. My first tutorial was this: Later, I wanted to model a spring system where a mass moving at a known velocity hits the spring. The governing equation and a similar modeling method given in the previous...