The Student Room Group

Edexcel Physics Unit 1 17th May 2012

Scroll to see replies

Mark scheme for as many Qs as can remember:
Multiple Choice: (NOT IN ORDER)
1 - Force
2 - Graph of potential/kinetic energy going straight down from left to right
3 - extension question was 2 delta X.
4 - mgh/t
5 - mg sin theta
6 - 0.56 Joules (i think it was around that might be 0.58)
7 - work = force * displacement (2 vectors give scalar)
8 - maximum stress at maximum stress of graph
cant remember the other two

Section B:
NOT IN ORDER
Newton's third law question:
An object exerts and equal and opposite force of the same type and magnitude on an object that exerts a force on it. The two forces were a third law example becasue:
Same magnitude (300N)
Same type
opposite direction
on two different bodies
same time

Terminal velocity question:
about 2ms-1

spring constant question:
about 31.97 Nm-1 i think

Viscosity question:
increase in viscosity decreases velocity
increase in temperature decreases viscosity so velocity increases

elevator speed question:
0.8 ms-1
graph was a triangle up to 0.8ms-1 at 2 seconds, straight line until 5 ms-1, and then same triangle down (-0.8 ms-1)

broken hook question:
brittle because it breaks with no plastic deformation so it doesn't change shape and can be fitted back together...

SUVAT
Horizontal:
2.13 i think (1.88/088)
Vertical:
4.27 ms-1?
Magnitude and angle:
IF 4MS-1 AND 2MS-1 USED, AS GIVEN:
63.8 degrees and 4.47 ms-1
IF 2.13 and 4.3 used:
64 degrees and 4.8 ms-1

Define laminar and turbulent:

Laminar - Parallel flow lines, no sudden change in speed or direction, no mixing of layers etc.

Turbulent - Mixing of layers, sudden changes of speed and direction and eddy currents formed etc.

Diagram - straight lines up to obstruction then mixing of lines past it

Last question about how you can tell that the elevator was going up:
- extension decreasing
- so coils must be getting closer together/being compressed

less than 3Joules question:
I got 2.38 Joules i think

question about how filming it benefited:
Allowed them to see results more accurately, i.e. can be slowed down and paused to see, for example, exactly how long it takes to reach maximum height etc.
Also, eliminated human error and different people have different reaction times so more reliable.

Question about labelling particle:
cant remember if it was going up or down:
If down: Weight down, upthrust and drag (viscous) upwards
If up: Weight down, drag down, and upthrust upwards
Equation connecting this:
If up: Weight + drag = upthrust
If down: Weight = drag + upthrust
(Now pretty sure it was going down)
Explain why it accelerates then reaches steady speed question:
let's say it was going down:
weight is greater than upward forces initially
but then upthrust and drag increase to equal weight so constant speed because no resultant force

That's all I can remember but some of it is bound to be wrong!!! so sorry!
(edited 11 years ago)
Original post by a10
Upthrust = Weight + Drag is constant velocity because the forces are balanced


Looking at my notes it was supposed to be Weight > Upthrust + Drag which implies its definately going down.

If the question said going up it would be Upthrust > Weight + Drag


No it's constant speed so if going up it would be

Upthrust = weight + drag
as no resultant force (Newton's first law, an object will remain at constant speed unless there is a res. force, and the question said that it was at constant speed didnt it?
Reply 442
Original post by youlostme
and about the pebble question....i said that as diameter inscreases, speed increases thats why the bigger ones reach bottom quick....is that right?


The question said assume all the densities of the rocks are the same(so those people who mentioned density wont get any marks)

looking at the stokes law equation F = 6 x pi x r x ita x v

the radius and volume are the only two things that will be changing so i said the pebbles had a smaller volume which would mean the force would be smaller(viscous drag force) hence the pebbles accelerate faster than the other particles because the bigger the object the more viscous drag it has and the faster an object travels the bigger the viscous drag...so because the pebbles volumes are ridicolously tiny the viscous drag would be negligible so they would accelerate faster hope that made sense! I hope its right :P
Reply 443
Resit number 2, incoming.
Reply 444
Original post by AGrumpyMole
No it's constant speed so if going up it would be

Upthrust = weight + drag
as no resultant force (Newton's first law, an object will remain at constant speed unless there is a res. force, and the question said that it was at constant speed didnt it?


yes one of the question said constant speed, in which case you should put Weight = Upthrust + Drag


which is constant velocity. Constant speed and constant velocity are the pretty much the same thing because there is zero acceleration
Original post by a10
yes one of the question said constant speed, in which case you should put Weight = Upthrust + Drag


which is constant velocity. Constant speed and constant velocity are the pretty much the same thing because there is zero acceleration


So was the particle moving down? i cant remember but using Weight = up. + drag it would be
(edited 11 years ago)
Reply 446
can anyone post the paper then i think we can work out the mark scheme :P
Reply 447
Original post by AGrumpyMole
So was the particle moving up? i cant remember but using Weight = up. + drag it would be

yeah constant velocity means its moving but at a real steady speed as the forces are balanced, velocity isnt changing in which case it would mean it was accelerating.(which is wasnt)
Original post by a10
yeah constant velocity means its moving but at a real steady speed as the forces are balanced, velocity isnt changing in which case it would mean it was accelerating.(which is wasnt)


I edited my post to say it would be moving down cos i put up by accident as its
weight = drag + upthrust
and drag acts opposite to the direction of travel so its gotta be goin down
Reply 449
man, just someone put up the damn unofficial mark scheme for this paper already!
appreciate the guy who did it earlier on but it didnt have everything
nope u guys are wrong it is the exponential one because air resistance acts on the object thrown .....so all gpe is not converted to KE ........because some of it is used up as work done against air resistance !! ...so it's definitely the exponential decay ....and we all know that (loss of gpe is never equal to gain of ke) unless they say something like no energy is lost to the surroundings !
Reply 451
Did any post an unofficial mark scheme ???
Reply 452
Original post by a10
The question said assume all the densities of the rocks are the same(so those people who mentioned density wont get any marks)

looking at the stokes law equation F = 6 x pi x r x ita x v

the radius and volume are the only two things that will be changing so i said the pebbles had a smaller volume which would mean the force would be smaller(viscous drag force) hence the pebbles accelerate faster than the other particles because the bigger the object the more viscous drag it has and the faster an object travels the bigger the viscous drag...so because the pebbles volumes are ridicolously tiny the viscous drag would be negligible so they would accelerate faster hope that made sense! I hope its right :P


I'm confused because I thought they were asking why the larger particles were at the bottom and why the smaller ones were at the top. Because I said that if you increase the radius then the velocity increases and so the larger particles move faster to the bottom.. ahhh i think i got it wrong :frown:
Original post by bilosoft
Did any post an unofficial mark scheme ???


I posted half of one on the other page
Original post by TJKerr
Newton's Third Law is that every force has an equal and opposite reaction force. So if a car is sitting on the road with no velocity.
Two forces will be occuring:

A force of the car on the ground

A force on the car from the ground (this is you reaction force if you want to think of it like that!)

These forces will also act 180 degrees to each other or act in completely the opposite directions :smile:



This should show you that Third Law pairs of forces will occur:

On different bodies (car and the ground)

Act at the same time

Be of the same type of force (gravitation, strong or weak nuclear, etc...)



Hope this has helped you and good luck for your exam!


Seen this post just before exam, ended up being very useful. Thanks
Original post by greywarden
nope u guys are wrong it is the exponential one because air resistance acts on the object thrown .....so all gpe is not converted to KE ........because some of it is used up as work done against air resistance !! ...so it's definitely the exponential decay ....and we all know that (loss of gpe is never equal to gain of ke) unless they say something like no energy is lost to the surroundings !


A physics teacher told me it was A, the straight line down, plus I saw it somewhere the other day.
The whole point was that Potential energy is lost at the same rate as kinetic energy is gained
(edited 11 years ago)
Reply 456
Original post by greywarden
nope u guys are wrong it is the exponential one because air resistance acts on the object thrown .....so all gpe is not converted to KE ........because some of it is used up as work done against air resistance !! ...so it's definitely the exponential decay ....and we all know that (loss of gpe is never equal to gain of ke) unless they say something like no energy is lost to the surroundings !


Let me tell you why, in my opinion, it can't be that particular graph, and therefore why it has to be the straight line by default:

- Let's assume it could be a curved line;
- The rate of energy transfer is directly proportional to the velocity with which the object is falling. This is because, the faster an object is falling, the faster it is loosing GPE and the faster it is gaining KE;
- The velocity of an object falling freely under gravity can never decrease;
- Therefore, the rate of energy transfer can never decrease (in any given second, the amount of GPE lost will either be the same or more than the amount of GPE lost in the previous second. Otherwise the object's velocity would be decreasing which is impossible. Make sure not to confuse acceleration with velocity);
- The rate of energy transfer is the gradient of the line representing the changes in energy;
- If the rate of energy transfer can never decrease, the gradient can never decrease, and therefore it can't be the curve that was in the question;
- Therefore, by default, it has to be the straight line.

Regardless of the answer, credit where credit is due - it was a good question. Don't worry though, the universe hasn't all gone wrong; the retarded question of how to keep your trousers from falling down with an elastic band more that balances things out! :P
What did you guys write for the Pebbles question?
I said something about how the diameter increases so as the diameter increases the weight/mass increases so they settle down at the bottom.. Not sure if it is correct though.
Reply 458
Original post by ShmangoBaby
What did you guys write for the Pebbles question?
I said something about how the diameter increases so as the diameter increases the weight/mass increases so they settle down at the bottom.. Not sure if it is correct though.


Density = (mass)/(volume) ---> mass = (density)(volume)

Density is same for all objects (as stated in question)

The pebbles have a larger diameter, therefore they have a larger volume. From the equation above, this means they have a greater mass.

Weight = (mass)(acceleration due to gravity)

Pebbles have a larger mass; equation above shows that is means they have a greater force of weight acting downwards.

Force = (mass)(acceleration) ---> acceleration = (force)/(mass)

Equation above shows that this means they accelerate downwards faster (due to the greater force of gravity), and therefore they reach the bottom of the jar first.
Original post by Top Hats
Density = (mass)/(volume) ---> mass = (density)(volume)

Density is same for all objects (as stated in question)

The pebbles have a larger diameter, therefore they have a larger volume. From the equation above, this means they have a greater mass.

Weight = (mass)(acceleration due to gravity)

Pebbles have a larger mass; equation above shows that is means they have a greater force of weight acting downwards.

Force = (mass)(acceleration) ---> acceleration = (force)/(mass)

Equation above shows that this means they accelerate downwards faster (due to the greater force of gravity), and therefore they reach the bottom of the jar first.


But surely you would have to mention the up-thrust and viscous drag? As the radius is increased, the resistive forces increase, hence this would decrease the resultant force? Therefore, acceleration would decrease.

Quick Reply

Latest