# Tag Info

### Including air resistance, what is the escape velocity from Earth?

Assume the initial velocity is v, assume a function exists v(t) that tells the velocity at time t. The derivative of this function is acceleration. Air resistance is 1/2pv(t)^2CdA (where Cd and A is ...
Accepted

### What happens if we fire a wooden bullet through a magnetic field?

Wood has a relative magnetic permeability (the ratio of a medium's permeability with that of vacuum) of almost exactly 1. The magnetic field will be almost completely undisturbed.
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1 vote

### How to create the function of an arrow being shot?

$$x=u_{x}t$$ $$y= u_{y}t + \frac{1}{2}at^2$$ Rearranging: $$\frac{x}{u_{x}} = t$$ Substituting into y: $$y= u_{y}\left(\frac{x}{u_{x}}\right) + \frac{1}{2}a\left(\frac{x}{u_{x}}\right)^2$$ If we want ...
• 4,376
1 vote
Accepted

### Acceleration of a projectile along an inclined plane

Question 1: Your $v_{x}$ and $v_{y}$ are not labelled correct. This does not represent the horizontal and vertical component relative to our original basis vectors. Using geometry the new basis ...
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### Acceleration of a projectile along an inclined plane

The statement "horizontal velocity is always is constant" is only valid if there is no inclined plane. Else it cannot be considered horizontal here, though it's horizontal with the inclined ...
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1 vote

### Acceleration of a projectile along an inclined plane

The horizontal velocity is constant. Notice that in the basis you're using, neither vector is horizontal or vertical. The easiest way to see it is to restart the exercise directly in another basis, ...
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### General relativity in layman’s terms (doubt)

Simply put, the motion of any object in spacetime follows what's called a geodesic. A geodesic is the shortest distance on a curved surface. Geodesics can be understood from a mathematical point of ...
• 303

### General relativity in layman’s terms (doubt)

Yes, the apple doesn't move but the Earth moves up to hit it. When you hold an apple still and let it go without giving it any force, it doesn't move (velocity is 0) just like Newton said in his first ...
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### General relativity in layman’s terms (doubt)

So let's say the picture depicts an apple thrown on earth surface. Those height markings must be moving upwards at accelerating rate, because they are at constant distance from the surface of the ...
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### General relativity in layman’s terms (doubt)

But I’ve heard that in general relativity, when you drop an apple, it’s velocity is 0 and it’s the earth that moves up ? What you have heard is incorrect. Strictly speaking, the Earth and the apple ...
• 33.9k

### Effect of height on artillery range

The extra height will give you more travel time before it strikes the ground, and hence more time to travel horizontally. In an ideal situation, the projectile maintains its horizontal speed until it ...
• 33.5k
1 vote

### Effect of height on artillery range

Assuming the projectile is fired at a 45 degree angle. Then the projectile will have an additional horizontal and vertical kinetic energies: KE_h=KE_v=\frac{KE_T}{\sqrt{2}}=mgh=\frac{\sqrt{2}}{4}mv^...
1 vote

### Lt. Joe Kenda's expertise(?) in fundamental physics

As to the observation that people tends to slump forward when they've been shot. When a person is standing upright most of of the weight of that person is carried by the forefeet. You can try that as ...
• 15.4k
1 vote
Accepted

### Lt. Joe Kenda's expertise(?) in fundamental physics

While bullets travel fast, they are extremely light compared to the mass of the human body, so they barely cause any backward motion on the victim. Let's do the math. Consider a $80\text{ kg}$ target ...
• 7,634

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