OCR Physics G484 - June 2013 Unit 4 (OFFICIAL RETAKE THREAD)

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Reply 160

Namod

Jan 2013 - Q5bi
dont get how pV is constant in the graph???

Reply 161

martynsteel

Original post by 9876543211

HELP please
A car of mass 1000kg is travelling at a velocity of 10ms-1. It accelerates for 15s, reaching a velocity of 24ms-1. Calculate:
a) The change in momentum of the car in a period of 10s
b) The average force acting on the car as it accelerates

I can get part b, i get 930N just putting numbers into equation F=m(v-u/t) but part a i cant get :L any help would be much appreciated :smile:

I saw that the answer is 1.4x10^4

Change in momentum = mv-mu

(1000*24)-(1000*10) = 1.4x10^4 :smile:

Edit: I accept that this doesn't incorporate the time but that's my best idea

(edited 10 years ago)

Reply 162

Namod

Original post by martynsteel

I saw that the answer is 1.4x10^4

Change in momentum = mv-mu

(1000*24)-(1000*10) = 1.4x10^4 :smile:

Edit: I accept that this doesn't incorporate the time but that's my best idea

you didnt read his next post

Reply 163

martynsteel

Original post by Namod

you didnt read his next post

Well it seems unlikely that there'd be a mistake (I saw this with a pinch of salt as our textbook is littered with errors).

Reply 164

Namod

Original post by martynsteel

Well it seems unlikely that there'd be a mistake (I saw this with a pinch of salt as our textbook is littered with errors).

you must really be martyn

Reply 165

martynsteel

Original post by Namod

you must really be martyn

What? That makes no sense...

Reply 166

HarryW95

Original post by abu125

why does a liquid have a generally higher specific heat capacity than solid?

Because for a solid to change state into a liquid, only a few bonds need to be broken between the atoms (less energy is required). However, for a liquid to change state into a gas, all of the bonds need to be broken so that the atoms are completely unconnected from each other (more energy is required).

At least I think that is correct.

Edit: Regarding the question above, that is an error in the book according to my teacher when we went through it.

(edited 10 years ago)

Reply 167

Kreayshawn

i don't see boyle's law or charles' law EXPERIMENT on the spec, do we really need to know the methods?
i can't even see charles' law written anywhere on the spec

Reply 168

Supes180

"select and use x = A cos(2 π ft ) or x = A sin(2 π ft ) as solutions to the equation a = – (2 π f ) 2 x" From the spec. What do they mean??

Reply 169

HarryW95

Original post by Kreayshawn

i don't see boyle's law or charles' law EXPERIMENT on the spec, do we really need to know the methods?
i can't even see charles' law written anywhere on the spec

I don't think so either. There won't be a question simply asking you to describe an experiment to demonstrate either of the laws, but they might have set up an apparatus and you may need to make comments using the knowledge of the law/ideal gases. For example, in January there was a question on the paper about how frequency and mass relate in a SHM experiment, which isn't on the spec but you have to apply what you know about SHM to answer it (if that makes any sense!)

Reply 170

HarryW95

Original post by Supes180

"select and use x = A cos(2 π ft ) or x = A sin(2 π ft ) as solutions to the equation a = – (2 π f ) 2 x" From the spec. What do they mean??

You use the sin equation when displacement begins at equilibrium position (on time axis on a displacement against time graph). You use the cos equation when it begins at the point furthest from equilibrium (the amplitude).

Reply 171

Lolc4

Original post by 9876543211

I would agree with the other posters and say that the change in momentum in total = (1000*24)-(1000*10) = 14000 and, as that's the total over 15s, assuming uniform acceleration the change in momentum after 10s would be (10/15)*(14000) = 9333kgms^-1

Reply 172

Chris2k13

Original post by Kreayshawn

i don't see boyle's law or charles' law EXPERIMENT on the spec, do we really need to know the methods?
i can't even see charles' law written anywhere on the spec

The two experiments we have to be able to describe are the 'Brownian motion' one and the 'Electrical determination of the specific heat capacity of a solid or liquid'.