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Author Topic: Edexcel PHYSICS Doubts  (Read 136188 times)

Offline Vampire-Love4ever

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Re: Edexcel PHYSICS Doubts
« Reply #390 on: January 09, 2011, 08:24:10 pm »
A car travels one complete lap around a circular track at an average speed of 100km/h.
(i)- If lap takes 3mins, show that the length of the track is 5km. I know this part :)

(ii)- What is the magnitude of displacement of the car after 1.5mins? <--- Explain how to do this, please!
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Offline Vampire-Love4ever

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Re: Edexcel PHYSICS Doubts
« Reply #391 on: January 09, 2011, 09:21:51 pm »
No one? :'(
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Offline astarmathsandphysics

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Re: Edexcel PHYSICS Doubts
« Reply #392 on: January 09, 2011, 10:34:59 pm »
One min
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Offline astarmathsandphysics

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Re: Edexcel PHYSICS Doubts
« Reply #393 on: January 09, 2011, 10:37:07 pm »
after 1.5 minc car has travelled halfway around the track so dsplacement =diammeter
5000=pi*diamter so diameter=5000/pi=1591m
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Offline Vampire-Love4ever

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Re: Edexcel PHYSICS Doubts
« Reply #394 on: January 10, 2011, 05:25:42 pm »
Quote from: astarmathsandphysics on January 09, 2011, 10:37:07 pm
after 1.5 minc car has travelled halfway around the track so dsplacement =diammeter
5000=pi*diamter so diameter=5000/pi=1591m

How do we know that we must use this?
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Offline blackberry

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Re: Edexcel PHYSICS Doubts
« Reply #395 on: January 10, 2011, 06:00:44 pm »
Quote from: Vampire-Love4ever on January 10, 2011, 05:25:42 pm
How do we know that we must use this?

you cant use 2.5km cuz that wud be the distance travelled not displacement.
they also mention that the track is circular so 5km is basically the circumference of the track
circumference formula--> C=2(pi)r
wen you solve the equation you get the radius as about 796 m. Double this to get diameter.
this will be the displacement.
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Offline blackberry

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Re: Edexcel PHYSICS Doubts
« Reply #396 on: January 10, 2011, 06:01:56 pm »
answer fast please!!!
what is the difference between air resistance and viscous drag???
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Offline The Golden Girl =D

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Re: Edexcel PHYSICS Doubts
« Reply #397 on: January 10, 2011, 06:05:49 pm »
it's almost the same. they both are OPPOSING forces.

if there is a balloon going UPWARDS , then the force opposing the motion is either viscous drag *the balloon is in a MEDIUM which is AIR* or air resistance.

I think they're the same.  CORRECT me if I'm wrong though.

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Offline blackberry

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Re: Edexcel PHYSICS Doubts
« Reply #398 on: January 10, 2011, 06:13:53 pm »
Quote from: Miss Invisible on January 10, 2011, 06:05:49 pm
it's almost the same. they both are OPPOSING forces.

if there is a balloon going UPWARDS , then the force opposing the motion is either viscous drag *the balloon is in a MEDIUM which is AIR* or air resistance.

I think they're the same.  CORRECT me if I'm wrong though.



hey so can air resistance act under water since there's air under water as well or will it just be called viscouse drag???
oooo do we have to learn the formula for terminal velocity of stuff in fluids or is it given in the paper??
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Offline The Golden Girl =D

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Re: Edexcel PHYSICS Doubts
« Reply #399 on: January 10, 2011, 06:22:01 pm »
Quote from: blackberry on January 10, 2011, 06:13:53 pm
hey so can air resistance act under water since there's air under water as well or will it just be called viscouse drag???
oooo do we have to learn the formula for terminal velocity of stuff in fluids or is it given in the paper??

1. Air Resistance has the Word AIR in it , which means it can't be AIR resistance if the object in in a liquid.

2. to be honest my teacher is ALWAYS Emphasizing on learning formulas.

I just checked June 2009 and the formula for the viscous drag*the one that has terminal velocity in it * is THERE !  but in my case ,I have Know it just like I know my name.

there is one that you might Not know though you MUST know it which is :

Terminal Velocity = {(2*r2*g) / (9 *eita) } * (Density of Solid - Density of Liquid)

Unit ->  m/s ;)

so ya :)
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Offline blackberry

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Re: Edexcel PHYSICS Doubts
« Reply #400 on: January 10, 2011, 06:25:02 pm »
thanxx man and yaa that was the terminal v formula i was referring to!!
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Offline The Golden Girl =D

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Re: Edexcel PHYSICS Doubts
« Reply #401 on: January 10, 2011, 06:28:52 pm »
I have difficulty learning that one -__- but we MUST know it.

your welcome =]
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Offline Vampire-Love4ever

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Re: Edexcel PHYSICS Doubts
« Reply #402 on: January 10, 2011, 08:38:41 pm »
Quote from: blackberry on January 10, 2011, 06:00:44 pm
you cant use 2.5km cuz that wud be the distance travelled not displacement.
they also mention that the track is circular so 5km is basically the circumference of the track
circumference formula--> C=2(pi)r
wen you solve the equation you get the radius as about 796 m. Double this to get diameter.
this will be the displacement.

The answer is 1.59km.

Method given:

Circumference= pi*D

5km= pi*D
D= 5km/pi = 1.59km

But I dont know why we must use this. :/
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Offline Vampire-Love4ever

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Re: Edexcel PHYSICS Doubts
« Reply #403 on: January 10, 2011, 08:43:34 pm »
I have a doubt.

I read from one of my photocopied notes that : the diameter of a wire should be measured using a micrometer screw gauge and calculate area using formula = 1/4*pi*d^2.

Is it right if we use formula: pi*r^2 instead? :S
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Offline Vampire-Love4ever

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Re: Edexcel PHYSICS Doubts
« Reply #404 on: January 10, 2011, 11:30:20 pm »
I am having my exam tomorrow!
Please help!

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