# 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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### Derivation of $V_f^2=V_i^2+2a\left(x_f-x_0\right)$

I'm reading this book on Classical mechanics, and they show a derivation of the mentioned kinematic formula: $V_f^2=V_i^2+2a\left(x_f-x_0\right)$ They start by saying that the acceleration of an ...
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### Determining the range of values for separation angle (Landau problem)

I encountered a problem while reading the following exercise from the second Landau & Lifshitz volume: Determine the range value in the $L$-system for the angle between the two decay particles (...
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Hi I was studying Aristotle motions law and comparing them with Newton. He states that heavier body fall faster than slow ones. I really can't understand how he could committed such a mistake...I mean ...
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### Proof of (Vi + Vf)/2

Its quite intuitive that when you have constant acceleration, the average velocity is given by (Vi + Vf)/2, but how can you prove it?
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I have a question about kinetic energy: Imagine two vehicles with velocities $v_1$ going at $30 \frac{\text{m}}{\text{s}}$ and $v_2$ at $50\frac{\text{m}}{\text{s}}$. If they hit each other, will ...
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So, the problem is straightworward when we suggest that air resistance force is constant: $$\vec F = \frac {\vec V_1 - \vec V_0} {t} m / b$$ $$\vec V_0, \vec V_1 - \text {initial and final ... 1answer 80 views ### Woman arrives 6s late for the train. Find her velocity to reach it [closed] A woman arrives exactly 6 seconds after a train leave the station at a constant acceleration of 0.4m/s^2. Find the minimum constant velocity she might run to get in the train. What I did: I wrote ... 2answers 56 views ### Problem with velocity vector [closed] Question: The radius vector of a point depends on time t, as \vec{r} = \vec{c}t+\dfrac{\vec{b}t^2}{2} where c and b are constant vectors. Find the magnitude of velocity. My attempt :$$\...
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I have come across a question that asked me to find the radius of curvature of a projectile. As far as I know, the path of a projectile is a parabola and I have found mention of the radius of ...
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### How do we calculate instantaneous velocity in 2D?

Suppose a body is moving with a constant speed of $10~\mathrm{ms^{-1}}$ in negative $x$ direction in $x$-$y$ plane. Let $\vec r$ be the position vector. Then what will be the instantaneous velocity ...
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### Kinetic energy dissipation in braking a vehicle

Let's say a vehicle that weighs 20t is hauling along at 50m/s and we want to brake it down to a full stop. The kinetic energy we need to dissipate into heating up the brakes is ...
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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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### Muting a bell with a resonating object

I recently moved into an apartment next to a church with bells and since then I haven't stopped dreaming of ways to mute them. I've been thinking about a design but I'm a little unsure of the ...
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### When considering the acceleration as constant? [closed]

I'm solving a simple dynamic exercise, exercise says: "What is the absolute value of the force necessary to speed up a 500kg mass subject to 1600km/h in 1,8s, with the object from rest?" Then I had ...
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### Is it right? time < 0?

I'm doing the solutions of Halliday's book kinematic exercise, given the equation of acceleration:$$a(t) = -30t.$$ One wonders when the acceleration is positive. In a resolution, says that for t < ...
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### A problem on rectilinear motion in a car [closed]

Today, I attempted the third question in the first chapter (Physical Fundamentals of Mechanics) in the book Problems in General Physics by I. E. Irodov. The question goes like this: A car starts ...
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### Why does the sound of my tea stirring go up in tone the faster I stir?

I've noticed that when stirring my tea, as I stir faster the tone generated by the stirring goes up. Why is that? Is it something to do with the Doppler Effect? EDIT -------------------------- ...
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### If velocity for an interval is zero then is acceleration also zero throughout?

We know that if velocity is zero for an instant, then acceleration need not be zero (a simple example of which is a ball thrown upwards.) But if velocity is zero for an interval, will ...
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### How do I set when the object isn't moving

I started studying instantaneous velocity derivatives using only now. It may seem stupid but really I'm not sure whether that's right: I have an equation: $$x (t) = 1.5t - 9,75t³$$ To set the time ...
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### How to locate the initial speed? [closed]

I have this question: Two men were delivering a crate of mass $100~\text{kg}$ to a house up a hill which is inclined at $35^\circ$, when it dropped and slid down the hill. The coefficient of ...
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