A gravity question about downward velocity of two items with different mass

[dynamicdude]

I have this doubt coming to my mind always.

I have two scenarios. I throw a small stone high up in the air and in another I shoot a bullet high up in the air. Now both of them will go to a point and come back with velocity pulled by gravity.

My question if the effect of both wil be same(assuming i throw the stone to the sameheight where the bullet reaches) ...And also whether the upward velocity will influence the downward push.

 

[flatulent]

Re: A gravity question?

In both cases you have a conservative field (the potential energy difference between tow points is independent of the path takien between them). The other aspect is conservation of energy. You give the object kinetic energy and it rises in the gravitational field which increases the potential energy.

 

[steve10]

Re: A gravity question?

1. When you are talking about "effect", what do you exactly mean? Different energies? Yes, they must be different if you assume the mass of a bullet is different from that of a rock. Here is the energy of the object at any moment:
E=0.5*m*v^2 + H*m*g
Notice that you got three parameters, v(velocity), m (mass) and H (height), any of them will affect the energy.

2. If both of them get to the same height and start to fall. It means that the initial velocities for both of them will be the same, 0, and the later velocities will be slightly affected by air friction. So, if the two objects (bullet and rock) are not projected too high, I don't expect their later velocities are so different. Secondly, according to your assumption, the heights for both of them are the same. Therefore, the only item that affects the energy is the MASS, which I suppose is quite different. Imagine how different a falling knife (might kill a fish) and a huge meteor (might trigger another tsunami) are.

 

[truebs]

Re: A gravity question?

Upward Velocity would have role only in the hieght the object travels ,but as u say that it reaches the same hieght, then it won't have an effect.

But one thing that could really make difference in the case of Bullet and a stone is the air thrust , as bullet is supposed to be more streamlined, it would come down slightly earlier than stone (if its rough ).

but this is not related to gravity , the gravitational force would be similarly acting on both bodies.

have i answered your question ?
Please explain a little bit more clearly your doubt if you need more explaination .

Anyways ...bye

 

[IrDA]

Re: A gravity question?

the key variable is mass in this situation as explained above with the formula

E=0.5*m*v^2 + H*m*g
Notice that you got three parameters, v(velocity), m (mass) and H (height), any of them will affect the energy.

since you have the same height and velocity for both objects then the only parameter to look at is mass.

All of the above apply without the thrust of air and the friction produced.

 

[Tinamuline]

Re: A gravity question?

First of all, your question is not quite clear. The word 'effect' as you mentioned may refer to the same height attained by both stone and the bullet. Suppose your assumption is acceptable (as a matter of fact, bullet can reach to a higher position in the air), both stone and bullet reach the same height, then they will fall onto the ground with the same final velocity provided that air resistance is negligible. Why do they fall onto the ground with the same final velocity? It is because by the principle of conservation of energy,
(PE + KE)i = (PE + KE)f
Since both objects have the same PE when they reach their same maximum height, then when they fall onto the ground, they should possess the same KE implying that they have the same final velocity.
In addition to this, since both objects are under the condition of free fall, they both subject to the same acceleration due to gravity, i.e. F = ma = mg . And that's why they have the same final velocity and this is what you call same 'effect'. I hope the above explanation can help you a bit. Please feel free to contact me should you have any problem. You are always welcome to ask me any physics question.
God bless you.

 

[A.Anand Srinivasan]

Re: A gravity question?

by saying that both reach the same height you just mean to say that they are given the same initial velocity (s=ut-1/2gt^2) so there is no difference in the situation itself