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A level Physics Materials/Mechanics Question related to Springs

I just need some help with understanding how this question can be solved, the Q is in the link, would be much appreciated

https://drive.google.com/file/d/1AQdx952XtROMC1OqfmU-D0wjNlE-v67h/view?usp=sharing
Hey!

Okay.

Consider the forces for the equilibrium condition we have before the string is snipped.

The spring currently supports three kilo's of mass.

We remove two of those three kilograms.

What will the forces involved be from the spring the instant that 2 kg is removed?

(I'm guessing you're fine with the 2 kg once it's free)
Reply 2
Avatar for kinghulio
kinghulio
OP
10
So the instant the sTring is cut, theres a force of 1g acting downwards due to weight of the 1kg mass. And the sPring still has a tension of 3g upwards from before the sTring is cut, so the resultant is 2g upwards.. F=ma then gives a=2g for the 1kg mass upwards.. Am I right? Feels like it but gotta be sure!
Reply 3
Avatar for kinghulio
kinghulio
OP
10
Original post by Callicious
Hey!

Okay.

Consider the forces for the equilibrium condition we have before the string is snipped.

The spring currently supports three kilo's of mass.

We remove two of those three kilograms.

What will the forces involved be from the spring the instant that 2 kg is removed?

(I'm guessing you're fine with the 2 kg once it's free)

So the instant the sTring is cut, theres a force of 1g acting downwards due to weight of the 1kg mass. And the sPring still has a tension of 3g upwards from before the sTring is cut, so the resultant is 2g upwards.. F=ma then gives a=2g for the 1kg mass upwards.. Am I right? Feels like it but gotta be sure!
yeah bro
Reply 5
Avatar for kinghulio
kinghulio
OP
10
Original post by Callicious
Hey!

Okay.

Consider the forces for the equilibrium condition we have before the string is snipped.

The spring currently supports three kilo's of mass.

We remove two of those three kilograms.

What will the forces involved be from the spring the instant that 2 kg is removed?

(I'm guessing you're fine with the 2 kg once it's free)

There is another Question I need help understanding, its to do with two springs in series and finding the energy stored in them. Would you be ok checking that out explaining it to me as well? Might as well get it cleared now. Heres the link

https://drive.google.com/file/d/1bAickKl08__EahNC_pT0JtoKkV1y_Y_H/view?usp=sharing

My answer was 0.6J, I thought that the spring constant would halve since they are in series, then I used f=kx to find the extension. I then subbed this into the equation for energy stored in a string which is E=1/2(Fx) where x is just extension
(edited 5 years ago)
Original post by kinghulio
There is another Question I need help understanding, its to do with two springs in series and finding the energy stored in them. Would you be ok checking that out explaining it to me as well? Might as well get it cleared now. Heres the link

https://drive.google.com/file/d/1bAickKl08__EahNC_pT0JtoKkV1y_Y_H/view?usp=sharing

My answer was 0.6J, I thought that the spring constant would halve since they are in series, then I used f=kx to find the extension. I then subbed this into the equation for energy stored in a string which is E=1/2(Fx) where x is just extension


They have the same force acting down each of them, so you just use the spring potential equation 0.5*k*A^2 = total PE at max extension for each. I think 0.6 is the right answer, I mean it should be.

In any case you have the right idea.
Reply 7
Avatar for kinghulio
kinghulio
OP
10
Original post by Callicious
They have the same force acting down each of them, so you just use the spring potential equation 0.5*k*A^2 = total PE at max extension for each. I think 0.6 is the right answer, I mean it should be.

In any case you have the right idea.


Ok, mark scheme says 0.3J but it maybe they took it as one spring even though the picture clearly shows 2. Anyway Thank you for your time, helped me alot!!
Original post by kinghulio
There is another Question I need help understanding, its to do with two springs in series and finding the energy stored in them. Would you be ok checking that out explaining it to me as well? Might as well get it cleared now. Heres the link

https://drive.google.com/file/d/1bAickKl08__EahNC_pT0JtoKkV1y_Y_H/view?usp=sharing

My answer was 0.6J, I thought that the spring constant would halve since they are in series, then I used f=kx to find the extension. I then subbed this into the equation for energy stored in a string which is E=1/2(Fx) where x is just extension


Original post by kinghulio
Ok, mark scheme says 0.3J but it maybe they took it as one spring even though the picture clearly shows 2. Anyway Thank you for your time, helped me alot!!


The spring constant 15 N/m is combined spring constant of the 2 springs. Working out the combined extension, you would get the extension as 3.0/15 m.
You can then work out the energy in the spring (combined springs) to be 0.3 J.
Reply 9
Avatar for kinghulio
kinghulio
OP
10
Original post by Eimmanuel
The spring constant 15 N/m is combined spring constant of the 2 springs. Working out the combined extension, you would get the extension as 3.0/15 m.
You can then work out the energy in the spring (combined springs) to be 0.3 J.

Cheers just looked at it again and it makes more sense. The wording is a bit annoying in these Q's sometimes though..

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