OCR Physics A G481 2015 Unofficial Markscheme

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Nuvertion
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Graphs

Velocity-time
Force-length (not extension (doesn't start through the origin), not original length (length changes))

Similar scalar quantities

Stress and pressure, Pascal or N/m^2. Alternatively stress and Young's modulus, same units.

Material properties

Polymer, doesn't obey Hooke's law, large elastic region, no plastic deformation, returns to original length when tensile/compressive forces are removed...

Input power of a motor

Attach a mass to the hanger of the motor (after measuring it). Measure the initial height of the mass using a meter ruler. Turn the motor on full power and simultaneously start a timer. After some time has passed stop the timer and the motor. Measure the new height of the mass. Input power = (mass * g * (new height - initial height) / time) / 0.15

Prove units of k

k = drag/(area*v^2)
drag = force [N = kgms^-2]
k = kgm * s^-2 * m^-2 * s^2 * m^-2
k = kgm^-3

Resultant of A and B

Sum their vertical and horizontal components separately. Construct a triangle from the result of the new components and use Pythagoras to find the resultant force.

Is B experiencing terminal velocity

No. Drag must but equal and opposite to weight. In this instance it's perpendicular to weight.

Assumption when calculating extension

The object obeys Hooke's law and only undergoes elastic deformation during the experiment (saying elastic deformation on it's own isn't enough, look at polymer materials). Alternatively the cross-sectional area is constant.
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Ngardnerpv
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sorry dude, honestly cant remember any of my numerical answers
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Nuvertion
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(Original post by Ngardnerpv)
sorry dude, honestly cant remember any of my numerical answers
Same here :| though the methods you used would help a lot.
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Throwaway6467
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Usually a teacher who has access to the paper after the exam will post an unofficial mark scheme on here.
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RBoss
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(Original post by Throwaway6467)
Usually a teacher who has access to the paper after the exam will post an unofficial mark scheme on here.
It is a lot easier that way
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j.greenwood98
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For scalar quantities for the same unit cant it be moment and torque?
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Nuvertion
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(Original post by j.greenwood98)
For scalar quantities for the same unit cant it be moment and torque?
Moment is a vector quantity as it has direction (clockwise or anticlockwise). Need to double check though, not 100% sure.
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MPH1997
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What was the assumption?


Posted from TSR Mobile
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tomzorz
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(Original post by MPH1997)
What was the assumption?


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I assumed it was that is undergoes only elastic deformation/no plastic deformation/obeys Hooke's Law
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John Fluffy Bunny
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(Original post by Nuvertion)
Graphs

Velocity-time
Force-length (not extension (doesn't start through the origin), not original length (length changes))

Similar scalar quantities

Stress and pressure, Pascal or N/m^2. Alternatively stress and Young's modulus, same units.

Material properties

Polymer, doesn't obey Hooke's law, large elastic region, no plastic deformation, returns to original length when tensile/compressive forces are removed...

Input power of a motor

Attach a mass to the hanger of the motor (after measuring it). Measure the initial height of the mass using a meter ruler. Turn the motor on full power and simultaneously start a timer. After some time has passed stop the timer and the motor. Measure the new height of the mass. Input power = (mass * g * (new height - initial height) / time) / 0.15

Prove units of k

k = drag/(area*v^2)
drag = force [N = kgms^-2]
k = kgm * s^-2 * m^-2 * s^2 * m^-2
k = kgm^-3

Resultant of A and B

Sum their vertical and horizontal components separately. Construct a triangle from the result of the new components and use Pythagoras to find the resultant force.

Is B experiencing terminal velocity

No. Drag must but equal and opposite to weight. In this instance it's perpendicular to weight.

Assumption when calculating extension

The object obeys Hooke's law and only undergoes elastic deformation during the experiment (saying elastic deformation on it's own isn't enough, look at polymer materials).
Don't you just draw a line from A to B to construct a vector triangle and then yay Pythagoras to work out its magnitude? Also I messed up the graph I've labelled it F against x overall I don't know if I'm even gonna get an a which is sad because when doing past papers I always used to get at least 90 percent
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Nuvertion
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(Original post by tomzorz)
I assumed it was that is undergoes only elastic deformation/no plastic deformation/obeys Hooke's Law
I don't think saying elastic deformation on it's own is enough. Polymer materials undergo elastic deformation but don't obey Hooke's law.
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Nuvertion
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(Original post by John Fluffy Bunny)
Don't you just draw a line from A to B to construct a vector triangle and then yay Pythagoras to work out its magnitude? Also I messed up the graph I've labelled it F against x overall I don't know if I'm even gonna get an a which is sad because when doing past papers I always used to get at least 90 percent
Pythagoras can only be used on right-angled triangles.
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1z3
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I stated that the assumption is that the cross-section area is constant throughout the metal strip.
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Nuvertion
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(Original post by 1z3)
I stated that the assumption is that the cross-section area is constant throughout the metal strip.
I believe that's another valid assumption.
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John Fluffy Bunny
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(Original post by Nuvertion)
Pythagoras can only be used on right-angled triangles.
Yeah i did that I believe I got root 5 by using the grid
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Nuvertion
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(Original post by John Fluffy Bunny)
Yeah i did that I believe I got root 5 by using the grid
teachercol is posting his mark scheme, forgot what the numerical answers were.
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tman96
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For the scalar quantities is torque and moments an answer
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Nuvertion
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(Original post by tman96)
For the scalar quantities is torque and moments an answer
No, they're vectors.
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nmjasdk
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(Original post by Nuvertion)
Graphs

Velocity-time
Force-length (not extension (doesn't start through the origin), not original length (length changes))

Similar scalar quantities

Stress and pressure, Pascal or N/m^2. Alternatively stress and Young's modulus, same units.

Material properties

Polymer, doesn't obey Hooke's law, large elastic region, no plastic deformation, returns to original length when tensile/compressive forces are removed...

Input power of a motor

Attach a mass to the hanger of the motor (after measuring it). Measure the initial height of the mass using a meter ruler. Turn the motor on full power and simultaneously start a timer. After some time has passed stop the timer and the motor. Measure the new height of the mass. Input power = (mass * g * (new height - initial height) / time) / 0.15

Prove units of k

k = drag/(area*v^2)
drag = force [N = kgms^-2]
k = kgm * s^-2 * m^-2 * s^2 * m^-2
k = kgm^-3

Resultant of A and B

Sum their vertical and horizontal components separately. Construct a triangle from the result of the new components and use Pythagoras to find the resultant force.

Is B experiencing terminal velocity

No. Drag must but equal and opposite to weight. In this instance it's perpendicular to weight.

Assumption when calculating extension

The object obeys Hooke's law and only undergoes elastic deformation during the experiment (saying elastic deformation on it's own isn't enough, look at polymer materials). Alternatively the cross-sectional area is constant.
I never found any angles to calculate compenents of A and B to find AB resultant. i just drew a line between the 2 points and measures its length, and used the scale 1cmm = 1km.

also whats this question about the assumption made in the experiement. i think i said something about constant area throughout the material somewhere in the paper, can someone remind me what that question was about again?
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John Fluffy Bunny
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(Original post by nmjasdk)
I never found any angles to calculate compenents of A and B to find AB resultant. i just drew a line between the 2 points and measures its length, and used the scale 1cmm = 1km.

also whats this question about the assumption made in the experiement. i think i said something about constant area throughout the material somewhere in the paper, can someone remind me what that question was about again?
Come on bro stop opening the old wounds
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