Official OCR Physics A G481 24th May June 2016

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This exam was actually quite alright, but how on earth do people finish in time? Everyone I spoke to in person said they ran out of time and left questions unfinished :|

I think I got 48-49/60, hopefully that's an A :s-smilie:

Reply 141

sqr00t

Original post by ludd-sama

What did you guys draw for the Force time graph on the drag question?

its constant at 0N from t=10s, though im unsure if the time before is an exponential decrease or an inverse exponential decrease

Reply 142

graciepi

I did an exponential decrease for the graph as D is proportional to v^2 so if you minus this D from the constant weight the resultant is an exponential decrease I think

Reply 143

sqr00t

Original post by cookie_raider01

yes exactly that

well clearly there's a difference between sitting on an air cushion/seat than sitting on bricks.... to make this difference more obvious, try throwing your arse on one of each :biggrin:

i'm sure one would hurt more than the other right?

Reply 144

cookie_raider01

Original post by sqr00t

well clearly there's a difference between sitting on an air cushion/seat than sitting on bricks.... to make this difference more obvious, try throwing your arse on one of each :biggrin:

i'm sure one would hurt more than the other right?

no same feeling :/

Reply 145

sqr00t

Original post by RBoss

I put surface area of downwards face of the parachutist, and air density instead of weight, due to some odd way in which the question was worded of something

i was doubting myself to put down weight or not so i decided not to put down weight.
and i only put down the surface area perpendicular to the line of action of the drag force.

Reply 146

Yougo132

I'm so pissed with that extension question. I believe the answer is 23mm, but I decided to divide by four at the end :/

Reply 147

sqr00t

Original post by RBoss

Did you say that the area had to be re-calculated after every weight addition? I didn't in the end but I guess the aluminium stretches with added weight

actually, i believe it is assumed that the area is constant. because aluminium is a rather brittle material (depending on its form, you wouldnt see aluminium as a ductile material anyways). so that means that until the sample breaks, then it still obeys hooke's law like behaviour as the elastic limit has not been exceeded. a brittle material is when theres little to no plastic region, so it would break at its elastic limit which would be the maximum stress.

Reply 148

sqr00t

Original post by RBoss

Did you say that the area had to be re-calculated after every weight addition? I didn't in the end but I guess the aluminium stretches with added weight

no, the area does not have to be recalculated after every weight addition. aluminium is a material that has little to no plastic deformation

Reply 149

sqr00t

Original post by 09johnsonda

Extension would decrease as the force increased and young modulus is constant so strain must be less because stress Is higher and young modulus must stay the same so as strain is less extension must be less

my brother, newton's third law pairs, the upwards acceleration is coupled with a downwards reaction force, and it is the reaction force which the cables experience, which would cause an extension.

Reply 150

Reda2

It was such an easy paper but I lost so many marks because I didnt get to do the last parts of the last question and the aluminium experiment thing.

How many marks was it for the finding the force constant or something experiment with the aluminium, and how many marks for the last questions from the extension question to the end? Thanks

Reply 151

sqr00t

Original post by graciepi

I did an exponential decrease for the graph as D is proportional to v^2 so if you minus this D from the constant weight the resultant is an exponential decrease I think

i was thinking in terms of each points on the vt graph, since the gradient is maximum at earlier times, that means the deceleration is maximum, and this gradient decreases quickly at first, but slowly after, so it would be exponential decrease until flattening.

Reply 152

_MAT_

Original post by Reda2

3 marks for the experiment

Second to last question was 3 or 4 marks I think and the very last question was 2

Reply 153

RBoss

Original post by sqr00t

i was doubting myself to put down weight or not so i decided not to put down weight.
and i only put down the surface area perpendicular to the line of action of the drag force.

That's a better way to phrase it - I just wrote down the first thing which sprang to mind because of the time rush. You had to state 2 things though

Reply 154

sqr00t

Original post by cookie_raider01

no same feeling :/

aye, so if we jump from 10 meters into water we would survive.
and if we jumped from 10 meters onto concrete floor, we would survive.

Reply 155

_MAT_

Original post by RBoss

That's a better way to phrase it - I just wrote down the first thing which sprang to mind because of the time rush. You had to state 2 things though

I don't think weight is a typically accepted answer, usually it's velocity, cross-sectional area, air density/temperature and surface texture I think

Reply 156

neyjunior

Original post by _MAT_

I don't think weight is a typically accepted answer, usually it's velocity, cross-sectional area, air density/temperature and surface texture I think

is there an unofficial MS for this?

Reply 157

sqr00t

Original post by Yougo132

I'm so pissed with that extension question. I believe the answer is 23mm, but I decided to divide by four at the end :/

i just wrote everything out like YM= (F divided by 4 for each cable/x-sectional Area of each cable)/(extension of a cable/32) then did math rearrangement to get 0.02325 or something, then divide by 10^-3 to get 23.3mm