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Author Topic: question on physics...have a doubt...  (Read 3638 times)

Offline helllife

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question on physics...have a doubt...
« on: November 10, 2009, 04:56:27 pm »
the question is....
A motor cycle goes from station A to B at 40km/h and then return from B to A at 120 km/h. Calculate average speed and average velocity during the round trip.

for average velocity it would zero, as the displacement is zero.....
but how the average speed is 60km/h??
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Offline falafail

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Re: question on physics...have a doubt...
« Reply #1 on: November 10, 2009, 05:18:39 pm »
Quote from: helllife on November 10, 2009, 04:56:27 pm
the question is....
A motor cycle goes from station A to B at 40km/h and then return from B to A at 120 km/h. Calculate average speed and average velocity during the round trip.

for average velocity it would zero, as the displacement is zero.....
but how the average speed is 60km/h??

don't you have to know the total distance and time taken to find the average speed?  :-\
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Offline helllife

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Re: question on physics...have a doubt...
« Reply #2 on: November 10, 2009, 05:26:26 pm »
well there is no other data given except the speeds mentioned above........do u how to do then?
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Offline Tyserius

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Re: question on physics...have a doubt...
« Reply #3 on: November 10, 2009, 05:28:17 pm »
I think you're missing something there.. You either need the distance from A to B or you just need the time he took to travel =/
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Offline helllife

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Re: question on physics...have a doubt...
« Reply #4 on: November 10, 2009, 05:36:44 pm »
isnt there any  other way? if anyone knows.......pls answer...
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Offline Tyserius

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Re: question on physics...have a doubt...
« Reply #5 on: November 10, 2009, 05:37:34 pm »
Average speed = Total distance travelled / Total time taken

So without the time / distance, you can't solve it =/
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Offline falafail

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Re: question on physics...have a doubt...
« Reply #6 on: November 10, 2009, 05:40:12 pm »
ohhh, okay. i get it.

let's assume the distance from A to B is d, so the total distance is 2d.
then, using d=st, you find that the time from A to B is d/40 and from B to A is d/120
so the total time = d/40 + d/120
and the average speed = 2d / (d/40 + d/120)
= 2d / (3d/120 + d/120)
= (2d x 120) / 4d
= 240d / 4d
= 60

;D
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Offline Tyserius

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Re: question on physics...have a doubt...
« Reply #7 on: November 10, 2009, 05:41:39 pm »
Quote from: falafail on November 10, 2009, 05:40:12 pm
ohhh, okay. i get it.

let's assume the distance from A to B is d, so the total distance is 2d.
then, using d=st, you find that the time from A to B is d/40 and from B to A is d/120
so the total time = d/40 + d/120
and the average speed = 2d / (d/40 + d/120)
= 2d / (3d/120 + d/120)
= (2d x 120) / 4d
= 240d / 4d
= 60

;D

Oh hahahaha! I forgot about the unknowns. Crap, Econs is lagging me behind for Physics T_T
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Offline helllife

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Re: question on physics...have a doubt...
« Reply #8 on: November 10, 2009, 05:53:44 pm »
oh....i got it!!! genius!!!! ;) ;)
Thanx ...will post question more later!! ;D
« Last Edit: November 10, 2009, 05:57:11 pm by helllife »
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Offline falafail

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Re: question on physics...have a doubt...
« Reply #9 on: November 10, 2009, 05:56:37 pm »
Quote from: helllife on November 10, 2009, 05:53:44 pm
oh....i got it!!! genius!!!! ;) ;)
Thanx anyways...will post question more later!! ;D

hah, well i'll try my best to help :)


Quote from: Tyserius on November 10, 2009, 05:41:39 pm
Oh hahahaha! I forgot about the unknowns. Crap, Econs is lagging me behind for Physics T_T

oh noes D:
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Offline Tyserius

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Re: question on physics...have a doubt...
« Reply #10 on: November 10, 2009, 06:36:54 pm »
Quote from: helllife on November 10, 2009, 05:53:44 pm
oh....i got it!!! genius!!!! ;) ;)
Thanx ...will post question more later!! ;D

Yes yes, post more as some kind of training for us for A Level xD

And @falafail : Well, I'm finally done with econs!
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Offline falafail

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Re: question on physics...have a doubt...
« Reply #11 on: November 10, 2009, 06:41:57 pm »
Quote from: Tyserius on November 10, 2009, 06:36:54 pm
Yes yes, post more as some kind of training for us for A Level xD

And @falafail : Well, I'm finally done with econs!

is this A level?! i thought it was IGCSE! D:
we don't get questions like this..  :-\


done studying or done with the exam, you mean?
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Offline Tyserius

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Re: question on physics...have a doubt...
« Reply #12 on: November 10, 2009, 07:18:55 pm »
Quote from: falafail on November 10, 2009, 06:41:57 pm
is this A level?! i thought it was IGCSE! D:
we don't get questions like this..  :-\


done studying or done with the exam, you mean?

Done studying xD And well, it does help us for A level in a way, I guess... If we're lucky we may get questions like this xD
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Offline falafail

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Re: question on physics...have a doubt...
« Reply #13 on: November 10, 2009, 07:20:48 pm »
Quote from: Tyserius on November 10, 2009, 07:18:55 pm
Done studying xD And well, it does help us for A level in a way, I guess... If we're lucky we may get questions like this xD

HA, you wish :P
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Offline Tyserius

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Re: question on physics...have a doubt...
« Reply #14 on: November 10, 2009, 07:21:23 pm »
Quote from: falafail on November 10, 2009, 07:20:48 pm
HA, you wish :P

Hahaha! Okay, I'm gonna try my best to get 30/30 for tomorrow! :D Go me!
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