Question

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Answer 1

Its solution is as follows: -




The shot is fired and the light is seen after 0.6 sec.
Since, the velocity of light is enormous.. you can neglect the time required by light to take a return trip to eye of observer.
So, basically the point is that the time taken by shot (shell) to reach target is 0.6 sec.
let the velocity of shell be v therefore s=v*0.6.......... (1)
Now, the sound is heard after 2.1 sec. so, the time taken by sound to reach observer after the explosion takes place is 2.1-0.6=1.5 sec
so, s=340*1.5
therefore s=510m
Putting this value in (1)
v=850 m/s

Answer 2

But I think that 'S' should be the distance from the burst to the observer
becoz the sound's travel is calculated from burst to the observer
so why S is taken as distance between tank & gun ??????????






This is my actual doubt.

Answer 3

Can anybody help me clearing my doubt ?

Answer 4

Please:)

Answer 5

the observer is at the tank and the burst happens at the gun. whats the doubt?

Answer 6

@telltoamit
amit sir
how did u come to know that observer is at the tank ?
I mean from which line of the question?

Answer 7

hellooo...i am firing a burst on a tank...obviously the guy observing it will be sitting inside the tank...

Answer 8

oh ok gt it.
thanx a lot:)

Answer 9

You're welcome :)

Answer 10

And, thanks for the medal

Answer 11

:)

Answer 12

i didn't understand one thing : why did we subtract light's time from that of sound's?

Answer 13

becoz the burst takes place after 0.6 seconds of tank's fire
& in an instant u see burst becoz light has ultimate speed.
but 2.1 sec. is the time from the tank's fire.
so 0.6sec. will be consumed upto the burst takes place then remains 1.5 sec
which is actually the time of sound
have u ever thought of hearing sound without burst?
so the sound will be after burst = total time - time for burst = 2.1 -0.6
=1.5
Do u understand now?
@Vaidehi09

Answer 14

remember that
2.1 sec. is the time from the tank's fire.

Answer 15

& sound will be after burst

Answer 16

but upto burst 0.6 sec is already consumed

Answer 17

so sound's time = 2.1 - 0.6 =1.5

Answer 18

got it or not ?

Answer 19

so, the bullet is shot. after 0.6 secs, u 'see' the burst. after 2.1 secs, u 'hear' the sound. but as u said, sound comes after the burst. so it should not include the time for burst anyway. or am i wrong?

Answer 20

ya u r right if u wanna say my way

Answer 21

Your clock is starting at t = 0.6seconds here

Answer 22

no @tel

Answer 23

@telltoamit

Answer 24

clock is starting at t=0

Answer 25

my bad, i mean u r not interested in whats happening before t = 0.6s

Answer 26

when u shot bullet; t=0
after 0.6 sec. bullet bursts boom!!!!
& after 1.5 sec of bullet-burst u heard sound
but actually from starting when the bullet was fired u can say time of hearing the sound is
0.6 + 1.5 = 2.1.
now gt it?

Answer 27

or any doubt?

Answer 28

but don't we need the distance between the 'gun' and the tank? not 'burst' and tank, right?

Answer 29

but gun is that target for burst
so gun = burst.

Answer 30

gt it?

Answer 31

but u said the burst take place 'after' 0.6 secs from firing. so it must have travelled some distance during that 0.6 secs, right?

Answer 32

ya of course

Answer 33

so how can the gun's position = burst's position?

Answer 34

I think u r confused at this point
that u r taking gun & tank same
but actually the are two armies one with tank & one with guns
so the tank fired a bullet at gun & the gun burst out:)
now gt it?

Answer 35

but the question says...gun fires at the tank!

Answer 36

oops sorry
reverse the names
& remaining is true.

Answer 37

reverse the names in my solution from where u asked ur doubt
& u will see that whole thing is true.

Answer 38

If u have any doubt then try to solve this in ur copy & then any doubt u can ask me:)

Answer 39

i think i still need some more time to grasp that idea. if i'm still confused, i'll have to trouble u again!

Answer 40

yeah of course:)
u can consult me .
but try this now please.

Answer 41

i mean, i am.

Answer 42

:)

Answer 43

@maheshmeghwal9 i got it at last!
what i had misunderstood was that we are observing the burst from the tank and that the burst is happening closer to the gun. now, i realize, that it was actually the opposite case!
this is what i understood:
bullet took 0.6 secs to travel from gun to tank. and the sound was heard 2.1 secs after the bullet was 'fired'. so 2.1 secs is not actually the total time travelled by the sound since sound originated at the tank, not the gun. so that's why we subtract 0.6 from 2.1 to get 1.5 which is the actual time for which sound travelled.
thanks a lot!! :))

Answer 44

oh now u r right 100%.
:)

Answer 45

:D yup, finally!

Answer 46

thanks, once again!!

Answer 47

:D

Answer 48

to aap bhartiya hain.

Answer 49

??

Answer 50

i think

Answer 51

yup.

Answer 52

i too:)

Answer 53

i figured :)

Answer 54

haha