finn26_
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Hey doing a past paper and I don't know how to answer this question:
A stone of mass 0.5kg is released from rest on the surface of the water in a well. The water exerts a constant resistance of 2N.

1. Find the acceleration of the stone

The stone takes 1.5 seconds to reach the bottom of the well.
2. Find the speed with which the stone hits the bottom,
3. The depth of water in the well.

Could someone please explain what to do because I am very lost.
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mqb2766
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If the water produces a constant force, what does that mean about acceleration?

(Original post by finn26_)
Hey doing a past paper and I don't know how to answer this question:
A stone of mass 0.5kg is released from rest on the surface of the water in a well. The water exerts a constant resistance of 2N.

1. Find the acceleration of the stone

The stone takes 1.5 seconds to reach the bottom of the well.
2. Find the speed with which the stone hits the bottom,
3. The depth of water in the well.

Could someone please explain what to do because I am very lost.
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finn26_
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I don't really know, i've never come across a question like this before.
(Original post by mqb2766)
If the water produces a constant force, what does that mean about acceleration?
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mqb2766
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How is force related to acceleration?
If it's constant, use SUVAT
If it's variable, use integration.
(Original post by finn26_)
I don't really know, i've never come across a question like this before.
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finn26_
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So do i just work it out the same way i would if it wasn't in water?
(Original post by mqb2766)
How is force related to acceleration?
If it's constant, use SUVAT
If it's variable, use integration.
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mqb2766
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As long as you account for the 2N force.
(Original post by finn26_)
So do i just work it out the same way i would if it wasn't in water?
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finn26_
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How do you do that?
(Original post by mqb2766)
As long as you account for the 2N force.
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Sinnoh
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(Original post by finn26_)
So do i just work it out the same way i would if it wasn't in water?
Almost every time in mechanics you can simplify it down to something very abstract. The well, the water, the air, the stone, it's all window-dressing. So you have to pick out the bits that actually affect it.
So once you know the acceleration, for the next few questions you're just using the suvat formulae. Depth means displacement, dropped from the surface means u = 0.
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mqb2766
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You have both gravity and water forces acting on the mass. How do they combine?
(Original post by finn26_)
How do you do that?
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finn26_
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I don't know i've never been taught about questions envolving water
(Original post by mqb2766)
You have both gravity and water forces acting on the mass. How do they combine?
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mqb2766
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You have gravity pulling the stone down and another force of 2N resisting motion .... so ...
(Original post by finn26_)
I don't know i've never been taught about questions envolving water
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finn26_
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Honestly I have no idea
(Original post by mqb2766)
You have gravity pulling the stone down and another force of 2N resisting motion .... so ...
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mqb2766
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What force does gravity exert on the mass?
(Original post by finn26_)
Honestly I have no idea
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finn26_
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10N
(Original post by mqb2766)
What force does gravity exert on the mass?
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mqb2766
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No, how did you get that?
(Original post by finn26_)
10N
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finn26_
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In our course we are told to take gravity as 10N
(Original post by mqb2766)
No, how did you get that?
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mqb2766
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The force depends on the mass.
The acceleration g is about 10 m/s^2
(Original post by finn26_)
In our course we are told to take gravity as 10N
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finn26_
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Ok, so how do i find the acceleration of the stone?
(Original post by mqb2766)
The force depends on the mass.
The acceleration g is about 10 m/s^2
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I understand the rest of the question i just don't know how to find acceleration. Could you please explain?
(Original post by Sinnoh)
Almost every time in mechanics you can simplify it down to something very abstract. The well, the water, the air, the stone, it's all window-dressing. So you have to pick out the bits that actually affect it.
So once you know the acceleration, for the next few questions you're just using the suvat formulae. Depth means displacement, dropped from the surface means u = 0.
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(Original post by finn26_)
I understand the rest of the question i just don't know how to find acceleration. Could you please explain?
The most important equation in all of mechanics: F = ma
where F is the resultant force
m is the mass
a is the acceleration

If you know the mass, you know the weight (weight is a force, mass is not)
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