Question

HELP !

Answer 1

yeahh u also ?

uhh i dont even knw where to start

Answer 2

Yeah I am.

Okay, Give me a sec.
I have done this question. :)

Answer 3

first problem i did it effortlessly... this one scares me

Answer 4

I think atlas will help you. :)

Answer 5

u know the best way to do such questions is to be an observer.................do u know anything abt inertial frames

Answer 6

u mean frame of reference, yes a bit.. pls explan i can catch up :)

Answer 7

Ok.......take it this way since both of them are travelling at the same velocity........if I am Mary and you are Alice......we both are practically at rest with each other

Answer 8

yes to start wid, before accelerating, go that :)

Answer 9

do you get this -i am talking as Mary....my frame of referance is Mary

Answer 10

*got

Answer 11

yes !

Answer 12

Now we are at rest with each other and the distance b/n us is 3m...........when you suddenly start accelerating at 1m/s^2

Answer 13

so your initial velocity u=0 (you were at rest w.r.t me)

Answer 14

a =1m/s^2

Answer 15

d =3m

Answer 16

oh initial velocity w.rt you is 0 yes ! i missed that beofre

Answer 17

I remember there being a formula which can help me find the time taken...........I hope u can do it now

Answer 18

u = 0
a = 1

Answer 19

but d, the distance between Alice & Mary is changing right?
its not fixed 3

Answer 20

When I am looking at Alice with my frame of reference.......the distance starts changing when Alice starts accelerating

Answer 21

yes

Answer 22

brb need to run a quick errand , but im realy desperate to understand this...
il be back in 20 mnts

Answer 23

k here is a magic formula................if you and I are the only people in the universe - we can give each other any velocity till the velocity given to both of us is equal (in both mag and direction) and by Doing this the laws of Physics for us will still remain the same. This is called Principle of relativity

In the question what I did is I gave both of them a velocity of -7m/s (opposite to their actual velocity) - Nothing changes by doing that since I have given them both the same velocity. Now they have come to rest and it becomes easy to solve the question then.

Answer 24

Tell me if this helps.. :)

Answer 25

your solution is perfect but a little longer way to do an easy question @AkashdeepDeb

Answer 26

observing through an inertial frame will make a lot of questions easy 4 u

Answer 27

I don't understand Inertial frames :/
HC Verma has also given it but it is tough to get. [FOR ME]

Answer 28

oh its ok you will get around to it in some time.
The concept is basically this - in physics everything is relative. I basically solved this question by sitting over Mary. if I sit on Mary I do not see Alice's velocity - because she is moving at the same velocity as mine. I just see her acceleration and the distance b/n us

Answer 29

you can sit in any frame that is at rest or at constant velocity - these are called inertial frames

Answer 30

understood that!
But how do you calculate using it?

Answer 31

oh if I do not see alice's velocity and I see only her acceleration and distance b/n us:
then : s = ut + 0.5at^2
u = 0 (her velocity w.r.t me is 0)
a = 1
s=3
you can find t

Answer 32

t = sqrt(6)
Same as your answer!!

Answer 33

OMG ! this method is too elegant and powerful !
@AkashdeepDeb ur method helped me understand how to approach...

thanks both :))