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S.W.A.T

by Aman verma » Tue Sep 21, 2010 11:56 pm
Q: A S.W.A.T Team commando fired two rounds ( Bullets ) at an interval of 335 seconds chasing at an uniform speed . A terrorist who was running ahead of the commando in the same direction, hears the two shots at an interval of 330 seconds . If the speed of sound is 1188 km/hr , then who is faster and by how much ?

a) commando , 22 km/hr

b) terrorist , 25 km/hr

c) commando, 18 km/hr

d) terrorist , 20 km/hr

e) commando, 14 km/hr
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by Maciek » Wed Sep 22, 2010 2:04 am
Hi Aman!

IMO C
If the terrorist hears the two shots at shorter interval than a S.W.A.T. Team does, the S.W.A.T. Team is faster.
It is because the distance between the S.W.A.T. Team and terrorist became shorter.
By how much the S.W.A.T. Team is faster?
x = (1 - 330/335)*1188 = (1 - 66/67)*1188 = 1188/67 = 17.7

Hope it helps!
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Maciek
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by pzazz12 » Wed Sep 22, 2010 5:13 am
Aman verma wrote:Q: A S.W.A.T Team commando fired two rounds ( Bullets ) at an interval of 335 seconds chasing at an uniform speed . A terrorist who was running ahead of the commando in the same direction, hears the two shots at an interval of 330 seconds . If the speed of sound is 1188 km/hr , then who is faster and by how much ?

a) commando , 22 km/hr

b) terrorist , 25 km/hr

c) commando, 18 km/hr

d) terrorist , 20 km/hr

e) commando, 14 km/hr

i think answer is C.
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by Aman verma » Thu Oct 07, 2010 9:56 am
Maciek wrote:Hi Aman!

IMO C
If the terrorist hears the two shots at shorter interval than a S.W.A.T. Team does, the S.W.A.T. Team is faster.
It is because the distance between the S.W.A.T. Team and terrorist became shorter.
By how much the S.W.A.T. Team is faster?
x = (1 - 330/335)*1188 = (1 - 66/67)*1188 = 1188/67 = 17.7

Hope it helps!
Best,
Maciek
Many thanks , Maciek !! , for clarifying the underlying logic.

Sol : 1188 x 335/330 - 1188 x 1 = 18 km / hr.

Logic : The difference in hearing of sound is basically the difference in the speed of sound at which it travels/reaches the terrorist.Such difference occured because the distance between the commando and the terrorist became shorter.The sound is travelling in it's own speed of 1188 km/hr but the discrepancy in reaching the sound to the terrorist is (335/330 - 1)

Hence OA[spoiler]C) 18[/spoiler]
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by aimscore » Tue Oct 12, 2010 2:22 pm
Hi Aman, Maciek

I did not understand how u guys reached (1 - 330/335).
Is there any underlying concept I need to know before solvng this problem?
would appreciate if you could explain the whole problem in detail.

Thanks
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by goyalsau » Wed Oct 13, 2010 9:05 am
Firstly I would like to thank you for posting such a awesome question.

I able to solve it in 26 minutes, and the best part is when i solved it once and then i was trying to recall , How i solved it ?
I didn't had the answer to my question.

So i thought its good to look for a shortcut and this is what i have to share with you

1188 x (1 - 330/335) = 18 km / hr.


Speed of air is 1188 km/hr

S = D/T

In one Second the speed will be 1188/ 60 * 60
To get the speed in one second.

Lets Call it as X

We have the new speed as X/sec.

Distance traveled in 335 seconds will be X * 335

Important thing to notice is First Bullet have to travel 335 Seconds and Second have to travel 330 seconds.
So there must be a difference in the distance that is traveled by both bullets.

Distance traveled by second bullet must be X * 330

Now (X * 335 - X * 330 ) = It will give us the distance between the places from where the bullet must have been fired.

Now it will be the same distance that the commando traveled in 335 seconds

So let commando speed be Y per second

(X * 335 - X * 330 ) = Y * 335 ( Because the commando must be running for 335 seconds before firing the second shot )


Now substitute the value of X

1188/ 60 * 60 ( 335 - 330 ) = Y * 335

Multiply by 60 * 60 Because we need the distance in per hour

1188 ( 335 - 330 ) = Z 335 ( Assume new speed is Z in km/hour )

its the same as 1188 ( 5/ 335 ) = 17.73



I have just given a try guys,
Please correct me if i am wrong any where in between.
Saurabh Goyal
[email protected]
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