Home » Ask & Discuss » Physics. » Optics « Back to Discussion

Optics

Blazing goIITian

Joined:	5 Nov 2007
Post:	507

29 Apr 2008 17:00:23 IST

0 People liked this

577

Mirrors and motion-assignment question

None

Question from my school assignment :

A car is fitted with a convex mirror of focal length 20cm.A second car is 6m away from this mirror.The latter starts overtaking with a relative velocity of 15m/s.How fast does the image move and in which direction?

Is the answer 0.14m/s?

Kindly give full solution..

Rates assured :-)

Share this article on:

Comments (7)

Celestine Preetham

Hot goIITian

Joined: 24 Apr 2008

Posts: 163

29 Apr 2008 20:26:19 IST

Like 1 people liked this

ans is 15\(29^2)

partially differentiate mirror eq to get ans

Learner .

Blazing goIITian

Joined: 5 Nov 2007

Posts: 507

30 Apr 2008 16:59:37 IST

Like 0 people liked this

I differentiated and got 0.015m/s..yours comes to 0.017m/s

or is there some mistake in my differentiation?

1/f=1/u+1/v

Differentiating wrt distance,

0=(du/dx)(-1/u^2)-(dv/dx)(1/v^2)

(dv/dx)(1/v^2)--15/u^2

dv/dx=-15*(v/u)^2

= -15(0.19/6)^2

=0.015m/s

Learner .

Blazing goIITian

Joined: 5 Nov 2007

Posts: 507

30 Apr 2008 17:00:57 IST

Like 0 people liked this

My initial answer was 0.014...by mistake typed it as 0.14..

anyway,did i make a mistake somewhere?

Thanks!:-)

Gaurav |spideyunlimited| Ragtah

Moderator

Joined: 16 Dec 2006

Posts: 3373

30 Apr 2008 17:20:57 IST

Like 1 people liked this

well I'm getting the same answer as you.
0.015 m/s

Celestine Preetham

Hot goIITian

Joined: 24 Apr 2008

Posts: 163

30 Apr 2008 19:22:18 IST

Like 1 people liked this

learner the error u made is finding V as .19 Its .1973684211
put V as UF/U-F to avoid approx

Gaurav |spideyunlimited| Ragtah

Moderator

Joined: 16 Dec 2006

Posts: 3373

1 May 2008 00:10:36 IST

Like 1 people liked this

yaar i used calculator still it comes as 0.015something

Learner .

Blazing goIITian

Joined: 5 Nov 2007

Posts: 507

1 May 2008 23:22:59 IST

Like 0 people liked this

Ok thanks guys...

The basic method is correct,right..I guess 0.015 and 0.017 difference can be neglected..

Thanks again!!

Quick Reply

Reply

	Some HTML allowed.
	Keep your comments above the belt or risk having them deleted.
	Signup for a avatar to have your pictures show up by your comment
	If Members see a thread that violates the Posting Rules, bring it to the attention of the Moderator Team