What Has Made You Laugh Today ?

[Jdsk]

Chatted about this in physics at school ..................

Stand on the roof of a train and fire a pistol towards the rear.
Train travelling at the muzzle velocity of the pistol.
Theoretical of course.

A person standing on the rail-side would see the bullet fall to the ground vertically.

At first I thought it would fall in a curve running in the direction of the train. The bullet reduces speed as it falls. But then again, you are right because the speed reduction would only occur because of air friction and as it is not pushing against the air there is no friction so it just falls.....unless the air is being dragged by the train, which it will, to a certain extent.....so...

Yes.

The question is posed so that the bullet has no horizontal speed relative to the ground. Gravity acts vertically downwards and it falls. And in the real world it would be pushed around by the air moved by the train, and by any wind.

Jonathan

[Jdsk]

833mph in 2012.

Faster than the speed of sound?
Explain please.

The one has been pushed to a point where the conditions need to be defined: what is she wearing, what attitude does she adopt, and what's the altitude?

But 120 mph is a sensible and commonly quoted value for the terminal velocity of someone who has fallen out of an aircraft or possibly from a very tall building.

Jonathan

[Maillot Rouge]

833mph in 2012.

Faster than the speed of sound?
Explain please.

No need to explain.
In 2012 the sound barrier was broken by a someone who jumped from a plane.
OK so it wasn’t a standard jump and it was set up as an attempt to do what they did but that’s the record.

[Cowsham]

Chatted about this in physics at school ..................

Stand on the roof of a train and fire a pistol towards the rear.
Train travelling at the muzzle velocity of the pistol.
Theoretical of course.

A person standing on the rail-side would see the bullet fall to the ground vertically.

At first I thought it would fall in a curve running in the direction of the train. The bullet reduces speed as it falls. But then again, you are right because the speed reduction would only occur because of air friction and as it is not pushing against the air there is no friction so it just falls.....unless the air is being dragged by the train, which it will, to a certain extent.....so...

Yes.

The question is posed so that the bullet has no horizontal speed relative to the ground. Gravity acts vertically downwards and it falls. And in the real world it would be pushed around by the air moved by the train, and by any wind.

Jonathan

What about the bullets acceleration ( decelerate) from minus muzzle speed ( what the train and bullet are doing before the trigger is pulled ) to zero?

Won't that contribute to the train speed and by how much? Obviously conservation of energy must be factored in since it took energy to accelerate ( decelerate ) the bullet. What will that do to the final speed of the bullet ?

These are the important questions we all MUST ask ourselves before we venture onto our bicycles for the day. ( especially me when I'm allowed back on mine )

[Jdsk]

At first I thought it would fall in a curve running in the direction of the train. The bullet reduces speed as it falls. But then again, you are right because the speed reduction would only occur because of air friction and as it is not pushing against the air there is no friction so it just falls.....unless the air is being dragged by the train, which it will, to a certain extent.....so...

Yes.

The question is posed so that the bullet has no horizontal speed relative to the ground. Gravity acts vertically downwards and it falls. And in the real world it would be pushed around by the air moved by the train, and by any wind.

What about the bullets acceleration ( decelerate) from minus muzzle speed ( what the train and bullet is doing before the trigger is pulled ) to zero?

Won't that contribute to the train speed and by how much? Obviously conservation of energy must be factored in since it took energy to accelerate ( decelerate ) the bullet.

It will have affected the speed of the train before the bullet leaves the muzzle. Assuming the question was referring to the speed of the train and the muzzle velocity at the moment that the bullet leaves the muzzle then it won't affect the trajectory of the bullet or the answer to the question.

Jonathan

[Jdsk]

Obviously conservation of energy must be factored in since it took energy to accelerate ( decelerate ) the bullet. What will that do to the final speed of the bullet?

Ever watched a film where the bullet knocks the victim backwards, through a window, up against a wall etc.

While the shooter holds the gun in one hand at arms' length?

And thought about conservation of momentum?

: - )

Jonathan

[Hellhound]

833mph in 2012.

Faster than the speed of sound?
Explain please.

No need to explain.
In 2012 the sound barrier was broken by a someone who jumped from a plane.
OK so it wasn’t a standard jump and it was set up as an attempt to do what they did but that’s the record.

A quick Google,do people know how to use Google and here's an explanation!
https://www.bbc.com/news/science-environment-19943590
Not a standard jump/freefall but he did hit 833mph and use a parachute
Some crazy people out there!

[Jdsk]

833mph in 2012.

Faster than the speed of sound?
Explain please.

No need to explain.
In 2012 the sound barrier was broken by a someone who jumped from a plane.
OK so it wasn’t a standard jump and it was set up as an attempt to do what they did but that’s the record.

If that's a reference to Baumgartner's jump in 2012 ... it wasn't from a 'plane.

https://en.wikipedia.org/wiki/Red_Bull_Stratos

Jonathan

[Hellhound]

If that's a reference to Baumgartner's jump in 2012 ... it wasn't from a 'plane.
https://en.wikipedia.org/wiki/Red_Bull_Stratos
Jonathan

Does it matter!?
It was a huge freefall/parachute jump.He jumped out of something really high and landed 10 minutes later using a parachute.On the way he broke the sound barrier.
Not a standard jump but a jump anyway!
Skydivers can hit almost 200mph,from a plane at standard heights,just by making themselves more aerodynamic.Terminal velocity for falling is 120mph.That is measured belly down with arms and legs wide.Alter the position to head pointed down with arms by the side and legs straight and although not 'falling' in the traditional sense,higher speeds can and are achieved.
Base jumping and Wing-suiting isn't from a plane either but they still use a 'chute

[Mick F]

Considering Earth is rotating at 1000mph at the equator, why don't you slam into a wall if you jump?

[Jdsk]

Terminal velocity for falling is 120mph.

And fall was the word used in the post that started this. And was ridiculed.

Jonathan

[Jdsk]

Considering Earth is rotating at 1000mph at the equator, why don't you slam into a wall if you jump?

"Newton's laws of motion":
https://en.wikipedia.org/wiki/Newton%27s_laws_of_motion

Jonathan

PS: And the same explanation works if you use the relativistic replacements.

[Mick F]

Good old physics eh?

Here's another one.
Powerful cannon on its plinth tilted at 45deg for max range.
Fires the cannonball half a mile where it hits the ground.

Put the cannon on a tall building, and do it again. Maybe gets two miles.
Put the cannon on a cliff 5000ft high. How far will the cannonball go?

How high would it have to be to put the cannonball into orbit?

[Jdsk]

Here's another one.
Powerful cannon on its plinth tilted at 45deg for max range.
Fires the cannonball half a mile where it hits the ground.

Put the cannon on a tall building, and do it again. Maybe gets two miles.
Put the cannon on a cliff 5000ft high. How far will the cannonball go?

How high would it have to be to put the cannonball into orbit?

Newton ran that as a thought experiment.
https://en.wikipedia.org/wiki/Newton%27s_cannonball



Jonathan

[Cowsham]

Considering Earth is rotating at 1000mph at the equator, why don't you slam into a wall if you jump?

Some times I do.