IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: WARRIOR on September 13, 2010, 04:44:01 pm

Title: AS Level Physics doubt.
Post by: WARRIOR on September 13, 2010, 04:44:01 pm: Weird question

The linear speed ( v in m/s) of a particle moving in a circular path depends on some or all of the following properties: r is the radius of the circle , w is an angular velocity in s^-1 with which the particle orbits about the circle , and m is the mass of the particle.There are no dimensionless constants in the equation.

What does 'There are no dimensionless constants in the equation.' mean?

(a) Find formula for v
is it just r/w?

(b) Find a formula for F , the force on a particle moving in a circle , which also depends on some or all of the above properties and also has no dimensionless constants.

Thanks in advanced

ps: If anyone can tell me what topic is this? Homogeneity?
Title: Re: IGCSE PHYSICS DOUBTS HERE !!!!
Post by: Dibss on September 13, 2010, 04:51:11 pm: Are you sure this is IGCSE? :/
Title: Re: IGCSE PHYSICS DOUBTS HERE !!!!
Post by: Vin on September 13, 2010, 05:01:16 pm: Quote from: Dibss on September 13, 2010, 04:51:11 pm
Are you sure this is IGCSE? :/

I know, right? :\

http://cnx.org/content/m14014/latest/

Kimo. This should help. However for only the (a) part. Do you know differentiation?

The answer is v = w.r
I have no idea how.
Title: Re: IGCSE PHYSICS DOUBTS HERE !!!!
Post by: WARRIOR on September 13, 2010, 05:10:22 pm: hmm thanks vin , thats a whole new topic i have to study.

And its AS PHYSICS (cambridge ) :/
Title: Re: IGCSE PHYSICS DOUBTS HERE !!!!
Post by: WARRIOR on September 13, 2010, 05:18:24 pm: Quote from: Percy Jackson on September 13, 2010, 05:14:58 pm
Well best of luck then. ;)

I'm splitting the post to create a new thread in GCE AS & A2 Level (CIE & EDEXCEL) board > Subject Doubts > Science. Some smarty pants might take a notice on it. ::) Is it OK?

yea sure you are MR . mod not me :P

so should i post my AS questions there from now ?
Title: Re: IGCSE PHYSICS DOUBTS HERE !!!!
Post by: Vin on September 13, 2010, 05:25:52 pm: Quote from: Kimo Jesus on September 13, 2010, 05:18:24 pm
yea sure you are MR . mod not me :P

so should i post my AS questions there from now ?

Yes, that'll be better. ;)
Title: Re: AS Level Physics doubt.
Post by: nid404 on September 13, 2010, 05:32:42 pm: Quote from: Kimo Jesus on September 13, 2010, 04:44:01 pm
Weird question

The linear speed ( v in m/s) of a particle moving in a circular path depends on some or all of the following properties: r is the radius of the circle , w is an angular velocity in s^-1 with which the particle orbits about the circle , and m is the mass of the particle.There are no dimensionless constants in the equation.

What does 'There are no dimensionless constants in the equation.' mean?

(a) Find formula for v
is it just r/w?

(b) Find a formula for F , the force on a particle moving in a circle , which also depends on some or all of the above properties and also has no dimensionless constants.

Thanks in advanced

ps: If anyone can tell me what topic is this? Homogeneity?

a)v=rw
b) F= mv²/r
Title: Re: AS Level Physics doubt.
Post by: WARRIOR on September 13, 2010, 05:41:18 pm: Quote from: Garfield on September 13, 2010, 05:32:42 pm
a)v=rw
b) F= mv²/r

can you explain the answers?
Title: Re: AS Level Physics doubt.
Post by: nid404 on September 13, 2010, 05:54:32 pm: Quote from: Kimo Jesus on September 13, 2010, 05:41:18 pm
can you explain the answers?

yeah :P

(http://www.mathwarehouse.com/trigonometry/radians/images/picture-s=r-theta-circle.gif)

angular velocity w= $\theta$ /t

s= r $\theta$

s=vt

v=s/t

v= r $\theta$ / t

$\theta$ / t=w

v=rw
Title: Re: AS Level Physics doubt.
Post by: nid404 on September 13, 2010, 05:57:28 pm: a= dv/dt

if theta is small, the dv/v=ds/r

ds=vdt=rd $\theta$ & dv=vd $\theta$

dv/v= vdt/r

dv=v²dt/r

dv/dt= v²/r

a=v²/r

F=ma
F=mv²/r
Title: Re: AS Level Physics doubt.
Post by: WARRIOR on September 13, 2010, 06:03:51 pm: wow man im shocked. thanks alot i owe you. Ill plus rep you later , but just one more thing, what does dimensionless constants mean?
Title: Re: AS Level Physics doubt.
Post by: nid404 on September 13, 2010, 06:17:07 pm: dimensionless would be something immeasurable. So what they're saying is the constants would be well defined.
Title: Re: AS Level Physics doubt.
Post by: WARRIOR on September 13, 2010, 06:21:35 pm: Quote from: Garfield on September 13, 2010, 06:17:07 pm
dimensionless would be something immeasurable. So what they're saying is the constants would be well defined.
i see, thanks. i have a lot of studying to do !
Title: Re: AS Level Physics doubt.
Post by: WARRIOR on September 15, 2010, 03:06:02 pm: i asked my physisc teacher and this is what i got , and it works !

We know that the unit of V = ms^(-1)

Also you have to know what angular velocity (w) is.w = radian per second ( rad s^-1)
form wiki the rate of change of the angular position of a rotating body; usually expressed in radians per second or radians per minute

if you dont know whats a radian (its very easy ) , follow this link : http://www.wisc-online.com/objects/ViewObject.aspx?ID=tmh1301

Radian is an angle ( 57.2 ) , angle has no UNITS. so in question it said no dimensionless quantities in equation! and angles have no unites therefore it is dimensionless and so the unit for angular velocity is just s^(-1)

and Lets go back to question of homogenity

V= ms^(-1)

and we have radius = m and angular velocty = s^(-1)

so to creat a formula that will be homogenous

V= r x w easier than it seems right?? ( so much xplanation was just for radian )

Part 2 of question

F = kgxms^(-2)

so we know the unit of M is KG , the unit of R= m , and the unit of w = s^-1

so F= m x r xw^2

all about homogeneity

i just have to check the 2nd answer with NID, ( garfield )