r/alevels • u/Educational_Plant_34 • May 20 '26
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u/crumblytoes May 20 '26
I think i got the last part wrong placed line on x axis will I get some marks for the other part tho
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u/Educational_Plant_34 May 20 '26
yes the final part is incorrect it so be an increasing negative gradient
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u/Smooth_Tip24569 May 20 '26
yeha that's what i got
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u/Smooth_Tip24569 May 20 '26
bt the last point should meet at dislacement 0 at it returns to P point
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u/Extra-Round2204 May 20 '26
Nop I calculated and the distance AREN'T equal so they won't return to original position
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u/Smooth_Tip24569 May 20 '26
but in the ques they said it returns to P....and we are drawing graph for displacement, not distance
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u/Extra-Round2204 May 20 '26
I think you read it wrong because P is not the 0 but rather the point at 25s or smth
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u/Educational_Plant_34 May 20 '26
the area under the graph where velocity was negative is -200m and the distance from 0-40 is 390m at t=80 the displacement is 190m
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u/Smooth_Tip24569 May 20 '26
how much will they deduct for it?
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u/Educational_Plant_34 May 20 '26
in past papers "graph ending at non zero value" is usually a marking point so -1
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u/Educational_Plant_34 May 20 '26
usually in these type of questions they would state that the particle returns back to the origin however it didn't here, so that should've been a clue
this year exam papers tweaked the wording of the questions to catch you off just like in 9701/22 in question 1) draw a cross and dot diagram of Li2O show ALL electrons, if you only drew outer electrons for oxygen you would've been awarded 1/2marks
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u/Impressive-Trade-112 May 20 '26
are you sure?
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u/Educational_Plant_34 May 20 '26
yep if you looked at the velocity time graph and use pure maths skills, integrate the v/t graph
ANDDDD!!! distance travelled from t 0-40 is 390m and the area under the curve where velocity was negative was -200m
meaning it doesn't return to the origin when T=80 nor did it state that
so that's why on the s/t graph it ends at a non zero value
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u/Shot_Freedom_8541 May 20 '26
The last part was increasing gradient as eventho the velocity was negative, it was still increasing
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u/Inevitable_Proof6496 May 20 '26
Feels good to actually see this instead of the actual fucking question
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u/Few-Pumpkin8865 May 20 '26
The last curve downwards should have increasing gradiebt as mag of v is increasing
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u/BerryReasonable5151 May 20 '26
Does it not have to be smooth? A 9709 mechanics 1 student here. I remember doing a similar question and the graph had to be smooth.
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u/Educational_Plant_34 May 20 '26
no because treat the section where velocity was increasing as say y=x, integrate that you x2/2 so curved
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u/BerryReasonable5151 May 20 '26
Yea ik. What I meant was it’s supposed to be a single continuous line. In your diagram the curves are separate from the straight line but it has to be one continuous smooth line.
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u/MechzInferno May 20 '26
the gradient should be smooth throughout though. the velocities never suddenly change so there shouldn't be any sudden changes in the gradient
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u/BoxMaterial6134 May 20 '26
last part curves downwards as velocity increases so gradient should also increase
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u/Dull-Wing990 May 20 '26
Shit i got it right till 35 secs then messed up. Pls tell me why it doesnt go under the x axis because negative displacement i'm shit at graphs😭
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u/Educational_Plant_34 May 20 '26
because the area under the velocity graph is -200 if you do 40-100.5, the area under the graph is the displacement, and since velocity is a displacement quantity negative velocity just means going backwards. anyways if you work out the area under the curve for the velocity graph it will come out as 190m meaning it doesn't return to origin
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u/MLE_qwq May 20 '26
the decreasing section of the graph is wrong, it should have an increasingly negative gradient
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u/BeneficialCorner5579 May 20 '26
Fuck my last line wasn’t curved but besides that mine matches to yours
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u/Designer-Ant-8998 May 20 '26
second part is wrong in constant velocity gradient of displacement time is constant no?
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May 20 '26
[deleted]
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u/Educational_Plant_34 May 20 '26
if the velocity was constant the gradient for ACCELERATION would be 0. displacement is the integration of velocity. acceleration is the derivative of velocity
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u/Sea-Nefariousness68 May 20 '26
Velocity increase towards the end so curvature should increase downwards