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Why should the stone weight matter here? Shouldn't the centripetal force and the Tension be equal?
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Why should the stone weight matter here? Shouldn't the centripetal force and the Tension be equal?
When talking about circular motion, the centripetal force should always be the net force on the object. This is why we need to take into account every single force on the stone, including its weight.Why should the stone weight matter here? Shouldn't the centripetal force and the Tension be equal?
So the weight also acts towards the centre?When talking about circular motion, the centripetal force should always be the net force on the object. This is why we need to take into account every single force on the stone, including its weight.
Why necessarily net force? Because Newton's Second Law demands that the F in F = ma be the net force, in every case; and in circular motion, centripetal acceleration and centripetal force also obeys Newtons Second Law.
Not always.So the weight also acts towards the centre?
As you mentioned above in the first reply, that the gravity of the stone is exerted on the glue. Could that be the reason why the weight should be included here ? Or am I looking at it the wrong way?Not always.
The weight always acts downward.
And since:
1. the centripetal force (F_c) is constantly changing direction as the object changes position
2. F_c = F + F_g ( F is the force exerted by the glue)
So...
The required magnitude of F is also changing.
And the largest F required corresponds to the "bottom" instant, where F_c is upwards and F_g is downwards (opposite to each other).
I think I explained that a bit vaguely at first.As you mentioned above in the first reply, that the gravity of the stone is exerted on the glue. Could that be the reason why the weight should be included here ? Or am I looking at it the wrong way?
I think I explained that a bit vaguely at first.
Let's start it again from the beginning. First, two things hold true at any moment:
1. F_c = F + F_g
2. F_g always acts downward
Now, since we know that a force has directions, that may affect its sign (positive / negative), let's suppose that, on the vertical axis, upward is positive, downward is negative.
F_g always acts downward, so we can say that F_g = - 3.0 N.
I know the question says that the stone's gravity is 3.0 N, without the negative sign. It actually means that the gravity has a magnitude of 3.0 N.
Here, the magnitude of something means the modulus, or absolute value, or that thing. For gravity, its magnitude means | F_g |.
We can also say that the magnitude of a force does not consider the force's direction, so it doesn't have a +/- discretion.
But once we start to consider directions, we need to use +/- signs to designate them. And surely you can designate downward as positive - either way is okay. But let's take upward as "+" for this time.
We know that F_c always acts towards the centre. And let's suppose that F_c has a magnitude of 10 N.
Then, when the stone is at the top, F_c is acting downward (centre is below the stone). At this moment, F_c = -10 N.
Based on F_c = F + F_g, we can get: -10 = F + (-3) --> F = -7 N then F has a magnitude of 7 N.
When the stone is at the bottom, F_c is acting upward (centre is above the stone). Then F_c = +10 N.
Again, using F_c = F + F_g, --> +10 = F + (-3) --> F = +13 N --> magnitude of F is 13 N.
You can see, at the top and the bottom, the gravity has opposite effects on the required magnitude of F.
This is why we need to take into account the stone's gravity.
P.S. We can also discuss on the moments when the stone is horizontally level with the centre (centripetal force acting horizontally), but that will involve the horizontal axis as well, and make things more complicated.
But if you are curious enough, we can discuss this in a separate chat.
mereko to kabhi bola hi nahi
teko already pata tha be -_-mereko to kabhi bola hi nahi
Okay, I now did understand the significance of including the weight but the equation that you have given here F_c = F + F_g and the equation you used in the first reply where the tension is 18N, and is equal to the sum of the stone's gravity and the centripetal force. My confusion is that are these two the same?
From the question
Tension(F) = 18N
Centripetal force(net force)(F_c) = ??
Weight of the stone ( here it's F_g) = 3.0N
Net force = F - F_g = 18 - 3 = 15N
So is it "F_c = F - F_g" OR "F_c = F + F_g" ?
Forget about that statement for a moment.
F_c = F + F_g is always the case, when the forces here are seen as vectors.
When the stone is at the bottom, centripetal force is upward, and gravity is downward. So F_c > 0, F_g = -3.0 N
So, plug in the value, we can see that F_c = F + (-3) --> F_c = F - 3
In the question,
- "tension is 18 N" actually means the tension's magnitude is 18 N, or |F| = 18 N
- "weight of the stone is 3 N" means |F_g| = 3 N
Now we know that F_g acts downward, but what's the direction of F?
F_c = F - 3 and F_c > 0 --> F - 3 > 0 --> F > 0
So F is upward. And since |F| = 18 N, we can say that F = +18 N
Then, at last, F_c = (+18) - 3 = +15 --> |F_c| = 15 N
/
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At this point, we have obtained the following:
|F| = 18 N
|F_g| = 3 N
|F_c| = 15 N
It's clear that |F| = |F_g| + |F_c|, or |F_c| = |F| - |F_g|
And this is actually what I meant by "tension is equal to the sum of the stone's gravity and the centripetal force", when we only look at the magnitude.
You should know all the basic knowledge of As and A level to apply it in paper 5.Aoa guys
I need advice on how to prepare paper 5 ? Could you just send me links of the resources to learn paper 5 and tips on how to prepare. I would greatly appreciate it !
Thanks in advance
Fb = bqv and Fe = qVView attachment 61563
(i) no change
(ii) upward
(iii) no change
can anyone plzz explain me the reason for these ans
yup.View attachment 61562
the ans of (ii) is no force ...is this because motion of particle is parallel to magnetic field?
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