- #1
No sir.Is this a homework problem?
Sir force is applied continuously perpendicular to the velocity as in case we rotates a stone using string and sorry I missed showing the force in my picture.OK. Well, your question is completely unclear. I can't figure out whether there is a small offset applied to the motion and then it is left alone over time (which is what your picture looks like) or a continuous small offset being applied constantly over time (as your question implies).
Sir can you please tell me from where can I get this proof.As @Bandersnatch notes, the problem is that you are allowing your velocity vector to change in your small time interval, but not the acceleration vector. If there's enough time for the velocity vector to change (possibly only infinitesimally) then there's enough time for the acceleration vector to change (possibly only infinitesimally). So the total acceleration in your ##\Delta t## won't be purely vertical, but will have a leftward component which will lead to it satisfying ##|\vec v_1+\vec v_2|=|\vec v_1|## (in the limit as ##\Delta t## goes to zero, anyway).
Someone else had the same question recently:Sir can you please tell me from where can I get this proof.
Sir I can't figure it from that thread can you please give me an proof of this.
Sir but in this derivation we have used the result of derivation"which proves that perpendicular force cannot change the magnitude of velocity" which is my question?Let ##K = \frac 1 2 m v^2 = \frac 1 2 m \vec{v} \cdot \vec{v}## be the kinetic energy of a particle. $$\frac{dK}{dt} = \frac 1 2 m \frac{d}{dt}(\vec{v} \cdot \vec{v}) = m (\frac{d\vec{v}}{dt} \cdot \vec{v}) = m\vec{a} \cdot \vec v = \vec F \cdot \vec v$$
Hence, if the force is perpendicular to the velocity, then ##\frac{dK}{dt} = 0##, which means the kinetic energy of the particle is constant, hence the speed is constant.
Sir but in this derivation we have used the result of derivation"which proves that perpendicular force cannot change the magnitude of velocity" which is my question?
Sorry to argue sir.
Whenever I see students with this misconception, they always look at the situation evolving forward in time. That is, they look at the velocity vector now, apply the [assumed to be] constant acceleration and derive that the velocity vector later has increased in magnitude. From this they conclude that speed must be increasing.As I have shown in the picture even if their is minimal change but shouldn't it increase after a long time as minimal changes will keep accumulating.
To decrease velocity magnitude, you need an acceleration component anti-parallel to velocity.As I have shown in the picture even if their is minimal change but shouldn't it increase after a long time as minimal changes will keep accumulating.
Sir can you please explain me this point I can't understand what you want to say.None of them ever bother to do the same calculation going backward in time to determine the velocity a moment ago. If they did, they would see that the speed a moment ago must also have been higher. So the same [mistaken] argument proves with equal force both that speed is increasing and that it is decreasing.
The SUVAT equations work equally well in predicting how a system behaves going forward in time and going backward in time. You can trace the trajectory of a stone on string or a planet in its orbit into the future or into the past.Sir can you please explain me this point I can't understand what you want to say.
Sir how can I apply it?How about applying that calculation to see how velocity behaves going into the past?
Look at your original post. You evolved the velocity forward in time as the object moved to the right under a constant upward acceleration. Go back and do it again. But now the object is arriving from the left under constant upward acceleration and arrives at the center with rightward velocity v. What must its velocity have been a moment ago?Sir how can I apply it?
Sir how can I apply it?
Your misunderstandings seem to go deep. Do you understand how a first derivative is defined? Do you understand limits? Tangent lines to a curve?Please help me get out of this problem, which is correct explanation of this.
So can you please tell me how can I give someone respect and as we can see most of the people on this thread are male so to whom may I say mam.Hemant, first, enough with the "Sir, if for no other reason than some of the "sirs" on PF are women.
It isn't necessary. Just talk to us like you would talk to a friend.So can you please tell me how can I give someone respect and as we can see most of the people on this thread are male so to whom may I say mam.
Some cultures put more emphasis on honorifics than others. Culture on PhysicsForums mostly follows current western forms, which means first names (or nicknames, for those of us not posting under our real names) for more or less everyone short of a head of state. Just say thank you at the end of the thread, and that's enough.So can you please tell me how can I give someone respect and as we can see most of the people on this thread are male so to whom may I say mam.
Firstly,I am not wasting someone time and if one thought that I am wasting his/her time then please just don't reply to my thread it's just that and secondly I thought a lot about a topic and sometimes I reply fast because I have seen or thought that explanation earlier so I tell them what is the place where I am stuck.Second, you are wasting the time of the people trying to help you as well as your own by not thinking about the answers you are gettng.
That run-on sentence could use a lot of punctuation. It accomplishes nothing but to disavow responsibility for your actions. A complete waste of electrons.I am not wasting someone time...
You do MUCH better than most of us would do in whatever your native language isI am really very sorry for my English and I accept my mistake, from now onwards I will do my best to explain what I write and also I want to tell that English is not my native language so I can't explain well in English.
That's an easy one. Just make sure your replies to what they say show that you have thought about what they have said - even if it seems to go against your preconceptions.So can you please tell me how can I give someone respect
Nicely put. Many of us just want to know that we are being listened to.That's an easy one. Just make sure you replies to what they say show that you have thought about what they have said
There is no feedback here to indicate that anything has been taken on board. There is no indication of what has been found wanting in any of the previously provided correct answers. There is only a renewed demand for a final answer.Please help me get out of this problem, which is correct explanation of this.