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

Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: mousa on December 04, 2009, 05:22:44 am

Title: Mechanics Questions
Post by: mousa on December 04, 2009, 05:22:44 am: well ppl i got a couple of Questions. see them attached below. hope you will help me as soon as possible., Thanks in advance.

Q 6 pg:57
Q 11 pg:58
Title: Re: Mechanics Questions
Post by: 123 on December 04, 2009, 08:15:43 am: forgot how q6 pg57 is done :P
I have done it b4, mayb try
resolving 2g vertically downwards (opposite to P & Q)
So for P & Q
P = 2gcos40
Q = 2gcos20
Though i don't think its simple as this!

Then q11 pg.58
Just resolve T & 2T vertically & horizontally
So
VERTICALLY: Tcos 60 + 2Tcos $\theta$ going upwards but 50N going downwards
Tcos 60 + 2Tcos $\theta$ = 50 ----------eq.1
HORIZONTALLY: T & 2T go in opposite directions: Tsin60 = 2Tsin $\theta$ ---------eq.2
For $\theta$ from eq. 2
Tsin60 = 2Tsin $\theta$
sin60/2 = sin $\theta$
$\theta$ = sin^-1 (sin60/ 2)

u know $\theta$ .....so find T from eq.1 !!

Hope this is right & clear
(PS: instead of a thanks plz give me +rep. power!! ;D)
Title: Re: Mechanics Questions
Post by: mousa on December 04, 2009, 10:23:30 am: Thanks alot... thoughQ6 isnt tha much clear.
anymore replies ?? astar??
Title: Re: Mechanics Questions
Post by: astarmathsandphysics on December 04, 2009, 10:46:38 am: In court today.
Title: Re: Mechanics Questions
Post by: astarmathsandphysics on December 04, 2009, 07:15:21 pm: res vertically Pcos 50+Q cos 20=2g
res horizontally Psin40-Qsin20=0 so P=Qsin20/sin40
P(cos50+sin20/sin40*cos20)=2g and P=2g/(cos50+sin20/sin40*cos20)
Title: Re: Mechanics Questions
Post by: astarmathsandphysics on December 04, 2009, 07:20:18 pm: res horizontally Tsin60 -2Tsinx=x so sinx=1/2 sin60=sqrt(3)/4
sub this into the equation below to find T
Res vertically Tcos 60+2Tcosx=50
Title: Re: Mechanics Questions
Post by: astarmathsandphysics on December 04, 2009, 08:12:03 pm: here
Title: Re: Mechanics Questions
Post by: mousa on December 05, 2009, 05:31:32 am: Quote from: astarmathsandphysics on December 04, 2009, 08:12:03 pm
here

Thanks alot sir, realy helpful, but how you assumed , all of the three forces, 2g ,p and Q act from the same point?? is that clearly ressembled by the diagram???
Title: Re: Mechanics Questions
Post by: astarmathsandphysics on December 05, 2009, 10:00:08 am: Yes. I resolved vertically and horizontally as shown.
Title: Re: Mechanics Questions
Post by: saifalan on December 05, 2009, 12:39:15 pm: Why are u being sued astar ??
Title: Re: Mechanics Questions
Post by: astarmathsandphysics on December 05, 2009, 12:47:22 pm: I sued barclays cos they cashed someone elses cheques from my account
Title: Re: Mechanics Questions
Post by: saifalan on December 05, 2009, 12:50:53 pm: Dammit, and I thought England was heaven.