# Tagged Questions

The description of the movement of bodies by their position, velocity, acceleration (and possibly higher time derivatives, such as, jerk) without concern for the underlying dynamics/forces/causes.

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### Find the initial velocity's angle of a projectile knowing only the ratio between the horizontal distance traveled and max height

The ratio between the horizontal distance traveled and the launch height is 3 to 1. I think it is possible to find the angle given this information, but how exactly do you do it? I think it's arctan(2/...
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### What happens if you fly a drone inside moving passenger airplane? [duplicate]

I have a little question. If I mark an X in the center of a passenger airplane, and try to fly a drone from the X mark in the moving passenger airplane (800-900 km/h), what will happen to the drone? ...
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### How to find the Average Speed in this question? [on hold]

If the average speed of a spaceship is 32,000 km/h, how long would it take to travel the 80 million km from Earth to Mars? I applied the S = D / T Formula and got 0.0004 h Because this is a ...
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### Find the Kinematic degrees of freedom of the following contraption

In the above mechanism it is required to find the generalized coordinates to write equation of motion of the MDOF system. I just want to ask how do we actually approach such a problem? How to identify ...
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### Defining Uniform Motion

According to Wikipedia the definition of motion is: In physics, motion is a change in position of an object with respect to time. Motion is typically described in terms of displacement, distance, ...
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### Average speed without given distance [on hold]

Here is the problem where the speed is given but not the distance and need to find the average speed.
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### How to find Tangential/Radial/Angular Velocity for motion in any curve?

Is the radial velocity responsible only for changing distance between objects and the component perpendicular to it only for change in direction? If so why? Please try to give a different explanation ...
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### Deriving the equation of motion for a rigid system

I want to derive equation of motion for the system shown in picture. How do I choose a generalized coordinate in order to calculate kinetic and potential energy of the system? I need the ...
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### What is acceleration of A and how to approach such accelerating pulley problem [on hold]

As shown in figure A and B are free to move pulley and rope are mass less, there is no friction at all between any two. Now my question is because of tension in rope, A will move left but how will B ...
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### Is running in a zigzag helpful in avoiding being shot by an arrow? [closed]

Two people A and B start at a certain point. B runs away from A to another point. A shoots arrows at B. Is it helpful for A to run in a zigzag rather than in a constant direction? To be more ...
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### General motion of a cone on an inclined surface

Suppose that a solid cone is placed horizontally on an inclined surface and is initially at rest. How will the cone move when it starts motion due to its weight? I know that its motion depends on the ...
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### Projectile motion from platforms of different height [closed]

So, I was thinking about the projectile motion example of an object launched from a Platform to the ground, and I started to wonder how you could calculate the example if the object was launched from ...
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### Projectile question doubt [on hold]

A hunter wants to shoot a monkey with an arrow by launching the arrow at a speed $v_0$ at a distance of $L$ from the base of a tree of height $H$ on which the monkey is sitting. Now on watching the ...
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### Simple change in velocity question

The hand of a clock is 1cm long. find the change in velocity of the hand in 15 seconds. The question is pretty simple, $v=2\pi R/T$ and then using the vector addition one can easily get answer which ...
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### Branching ratio for a bound state

Consider the meson $\Upsilon(10860)$. It decays into $B\bar{B}$, $B\bar{B}^*+cc$ and $B^*\bar{B}^*$. The mass of $B$ is $5.28 ~\textrm{ GeV}$ and mass of $B^*$ is $5.33~\textrm{ GeV}$. The branching ...
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### How can an object's instantaneous speed be zero and it's instantaneous acceleration be nonzero?

I'm studying for my upcoming physics course and ran across this concept - I'd love an explanation.
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### A car is moving with constant acceleration at 2 m/s/s. what distance will it have travelled when its velocity is 8m/s [closed]

a car of length 3m is moving with constant acceleration at 2 m/s/s. How far will its front end be from the start point when its velocity reaches 8m/s The cars back end is on the start point and its ...
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### Kinetic energy of a suspended mass from an overhead crane [closed]

I am using Lagrange's method to formulate the equation of motion for a 3D overhead crane that is shown below: For the formulation of the kinetic energy for the payload (suspended) mass. I have seen ...
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### Solar Sail Questions

I'm just looking for a good (better) analogy. How do massless photons put pressure on a surface especially when it's a mirror? Using the analogy of the wind (atmosphere) on a sail breaks down when I ...
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### Point object, Kinematics

I am very new to physics. This evening, I was reading about the concept of objects to be considered as point objects under some circumstances. And I was trying to think of circumstances under which ...
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### HELP WITH PHYSICS NUMERICALS? [closed]

Okay so ive a test tomorrow and i cannot get my head around these questions. Any help? :D A starts travelling from London to Paris at 8AM at 60mph. B starts following Aat 11am and catches A in 4 ...
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### How do you arrive at this equation? $\bar{v} = v_2 - \tfrac{1}{2} a \Delta t$

$$\bar{v} = v_2 - \tfrac{1}{2} a \Delta t$$ $\bar{v}$ being average velocity and $v_2$ instantaneous velocity at one point this equation was used to find instantaneous velocity from average ...
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### A projectile is thrown at angle θ with an inclined plane of inclination 45o . Find θ if projectile strikes the inclined the plane horizontal [closed]

My attempt: Vx=ucosθ - gsint(45)t Vy=usinθ - gcos(45)t These are the velocities after time t. Vx=Velocity along the plane after time t. Vy=Velocity perpendicular to plane after time t. As at the ...
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### How can I find the maximum height if I have changing acceleration?

I'd like to find the maximum height that a projectile reaches in motion if I have a non-constant acceleration. How would I do this? What variables do I need to know in order to calculate this? ...
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### How to calculate impulse force of body hitting water?

I'm calculating the force of a body hitting water from a high height. So far I've figured out the velocity at the time of collisions would be 40 m/s. The body is 78 kg. I seem to need the time it ...
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### Extra vibrational mode in linear molecule

When calculating the number of vibrational modes for a molecule, the formulas differ for linear $(n = 3N - 5)$ and non-linear $(n = 3N - 6)$ molecules, where $n$ is number of modes and $N$ is number ...
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### Is it possible to determine particles' velocities from their crossings on a ring?

2 particles are constrained to move in a ring. Both particles begin moving at $t=0$ from $p=0$, each particle moving in the opposite direction of the other. It is known that they are moving at ...
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### In perfect vacuum (no external force), if I apply a small amount of force to a body, will it continue to accelerate forever?

According to the equation $F = ma$, the greater the force applied to a body, the greater its acceleration. But in a place where there is no gravity or any other kind of external force, if I apply a ...
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### Explanation about friction force directions of two moving bodies in contact

can someone explain me why in this scenario (picture below) we have a friction force Ftr12 in the same direction as movement (left part of the picture, case 1 ) and how these directions of friction ...
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### Projectile, air resistance and wind

So for my school project I am working on a projectile simulator and air resistance. So I have looked at this. Equations for an object moving linearly but with air resistance taken into account? ...
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### Acceleration velocity relation

I just happened to come across this specific question in physics:- Q: If a particle is moving along a straight line with increasing speed, then, (1) its acceleration is negative (2) its ...
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### Why does $k^z/E$ have dimensions of inverse velocity rather than velocity?

I'm studying quantum field theory and I want to prove the cross section. In Peskin's book, equation 4.77 says that:  \frac{1}{\left | \frac{k_{A}^{z}}{E_{A}}-\frac{k_{B}^{z}}{E_{B}}\right |}=\frac{...
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### Intercept of 2 moving objects at constant acceleration

I have to make a simulation in which a guided missile has to hit an incoming enemy missile.The enemy missile "T" is the one which has to be intercepted and is only affected by gravity, the guided ...
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### Area under the displacement-time graph giving time?

This is probably very stupid, but today at a lecture, our professor solved a problem where we had to find the time taken to travel from 0-5m, where $v = 3/x$ (velocity is a function of position.) ...
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### Why there is a $\frac{1}{2}$ in the distance formula $d=\frac{1}{2}at^2$?

I'm preparing for my exam, but I have difficulties in perceiving why there is a $\frac{1}{2}$ in the distance formula $d=\frac{1}{2}at^2$?
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### Velocity ; Acceleration [closed]

A ball was thrown vertically upwards with a speed of 3m/s. The ball reached a highest point before falling down to the ground. What is the acceleration of the ball at the highest point? A 0m/s2 B ...
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### Explain $\Delta x = v_0t + \tfrac{1}{2}gt^2$ please? [duplicate]

$g = \Delta v/t$, so $\Delta v = gt$. $v = v_0 + \Delta v$, so $v = v_0 + gt$. So if $\Delta x = vt$, then $\Delta x$ should be $v_0t + gt$. Why the $\tfrac{1}{2}gt^2$? I'm really confused, so this ...
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### Acceleration at rest when ball is thown [duplicate]

If a ball is thrown vertically upward and it comes to rest for a moment, then its velocity decreases and becomes zero. Does its acceleration also becomes zero? If yes then how ball falls down?
Two photons traveling along the x-axis (in a lab frame of reference) of different frequencies are about to collide. Their 4-momentum vectors are (h$\nu_1$/c , h$\nu_1$/c , 0, 0) and (h$\nu_2$/c , -h\$\...