Energy (potential/kinetic) in a VERTICAL mass-spring system

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Teenage Hype
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#1
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http://zonalandeducation.com/mstm/ph...OnASpring.html

This site has conflicting information with question 3(b) of this paper:

http://filestore.aqa.org.uk/subjects...2-QP-JUN14.PDF

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Ok, at the bottom GPE is at a minimum and EPE is at a maximum fine, and the opposite is true for the top, GPE at a maximum and EPE at a minimum.

But why at the midpoint on the question is potential energy ZERO? Wouldn't it have GPE and epe equal to the difference between the maximum and the minimum?

Instead it says the total potential energy is zero, which is confusing, because energy is a scalar not a vector. I understand that force is zero due to gravity and spring force cancelling each other out (hence why velocity and kinetic energy is maximum at the midpoint). But I cannot see why potential energy is zero.

Would appreciate some help asap!
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Kyx
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(Original post by Teenage Hype)
http://zonalandeducation.com/mstm/ph...OnASpring.html

This site has conflicting information with question 3(b) of this paper:

http://filestore.aqa.org.uk/subjects...2-QP-JUN14.PDF

-----------------------

Ok, at the bottom GPE is at a minimum and EPE is at a maximum fine, and the opposite is true for the top, GPE at a maximum and EPE at a minimum.

But why at the midpoint on the question is potential energy ZERO? Wouldn't it have GPE and epe equal to the difference between the maximum and the minimum?

Instead it says the total potential energy is zero, which is confusing, because energy is a scalar not a vector. I understand that force is zero due to gravity and spring force cancelling each other out (hence why velocity and kinetic energy is maximum at the midpoint). But I cannot see why potential energy is zero.

Would appreciate some help asap!
In the middle of the oscillation the potential energy is at minimum and the kinetic energy is at maximum


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Teenage Hype
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(Original post by Kyx)
In the middle of the oscillation the potential energy is at minimum and the kinetic energy is at maximum


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But does that mean it is zero? Since the mass is above it's lowest point, it will have some gravitational potential energy?
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Joinedup
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(Original post by Teenage Hype)
But does that mean it is zero? Since the mass is above it's lowest point, it will have some gravitational potential energy?
its the total potential energy so it's the sum of GPE and EPE...

the zero point has Imo been chosen for convenience, since you're interested in the size of changes in PE between different points on the pendulum's travel there's nothing wrong with that.
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Teenage Hype
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(Original post by Joinedup)
its the total potential energy so it's the sum of GPE and EPE...

the zero point has Imo been chosen for convenience, since you're interested in the size of changes in PE between different points on the pendulum's travel there's nothing wrong with that.
Fair enough I guess. Confusing question though, but I understand it now (conservation of energy).

Thanks!
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