URGENT HELP

- DominantVampire

URGENT HELP

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- DominantVampire

a block of mass 12 kg is released from rest om a friction-less incline of the angle theta=30
below the block is a spring having spring constant 10^4 N/m. the block stops momentarily when it compresses the spring by 4 cm. how far does the block move down the incline from its rest position to this stopping point

- DominantVampire

does anybody know

- DominantVampire

@ganeshie8 @Compassionate @mathmate @mathmath333

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## More answers

- DominantVampire

just*

- DominantVampire

i asked this sol. many times but each time the FORMULA is different

- DominantVampire

q*

- DominantVampire

irish boy come to physics department in my Q which you already answered but what youve answered is energy not the distance, please look other solutions too, i am getting diff. ans

- DominantVampire

- anonymous

why urgent?

- IrishBoy123

there does seem to be some confusion about this.
the first thing you need to do always is to draw it - and yes i could probably do this in my head but i would still always sketch it in outline just to be sure. that not only aids communications between you and others but will help you get the problem clear in your mind and it will also be a place to define variables such as vertical distance and distance along the slope - which are important here.
you should do that first using the "Draw" widget that OS provides
after that we can work through it.

- DominantVampire

oka

- DominantVampire

|dw:1434455352074:dw|

- IrishBoy123

yeah!!
|dw:1434455454721:dw|
this is what i mean by adding in other data.
make sense?

- DominantVampire

yes it does

- IrishBoy123

so "frictionless" means no energy lost to friction/heat, yes?
that means we are looking at loss of grav potential energy of block which converts to potential energy in spring. simplest way to do it. is that what you are after?

- DominantVampire

yes that's what it mean and that's what i'm after

- IrishBoy123

why not makes it easy for now just by calculating the energy in the spring when it is compressed 4cm. just work that out.

- DominantVampire

1/2kx^2?

- IrishBoy123

yes

- DominantVampire

oka so this is the first step? 1/2 (10^4)(4)^2

- IrishBoy123

mmmm.
units?
maybe this is where you are going wrong?

- DominantVampire

convert 4 cm into mterers so 0.04 m the ans i get K.E= 8J

- DominantVampire

joule

- IrishBoy123

|dw:1434456031864:dw|

- DominantVampire

i said that

- IrishBoy123

8J here too
all good so far
now that is the grav potential energy the block lost by sliding down the slope.
we need now calc h -- see the diagram. know how to?

- DominantVampire

U= mgh ? perhaps the P.E

- DominantVampire

i dont know, sighs, thats where i get confused perhaps we use energy conservation formula

- IrishBoy123

looks good. do the sums and we can compare results.
do you use g = 10 or 9.8?

- DominantVampire

9.8 to be exact

- DominantVampire

how to find h? where U= mgh U is??

- DominantVampire

we might resolve into its components ?

- DominantVampire

mgh sin theta

- IrishBoy123

look at diagram where i marked "h" in. that is what we want. make sense?
mgh = 8J

- DominantVampire

oh so U=K i see (12)(9.8)h= 8 so h is 0.06 m

- IrishBoy123

check your calculator: 0.06 m ? i get 0.068 which is closer to 0.07.

- DominantVampire

yes yes it was

- IrishBoy123

|dw:1434456513348:dw|
so this is where we are, and another litle sketch to make sure we understand what is happening
do you agree with this?

- DominantVampire

yes it right

- IrishBoy123

and question asks:
"how far does the block move down the incline from its rest position to this stopping point "
do you see it? what is the answer?

- DominantVampire

mmm no, i dont. im sorry

- DominantVampire

the answer is h?

- IrishBoy123

|dw:1434456741787:dw|
to lose 8J of PE, the block had to fall 0.068m vertically. that involved travelling distance d down the slope.
so this now becomes a simple trig problem....

- IrishBoy123

do you know trigonometry? sin, cos, tan and the rest?

- DominantVampire

oh yes im sorry

- IrishBoy123

you have the opposite, you want the hypoteneuse, sohcahtoa....

- IrishBoy123

we're close, are you still there or wanna finish later?

- DominantVampire

im sorry there was a power cut

- IrishBoy123

well, fire away. use trig and get d from h = 0.068 and angle = 30degrees

- DominantVampire

it would be dsin30=h so 0.07/sin30

- DominantVampire

is it correct

- IrishBoy123

yes, in cm, d = 13.6cm

- DominantVampire

0.136 m

- DominantVampire

i saw this ans. somewhere else too, let me show you, please do visit

- DominantVampire

@IrishBoy123 thankyou so so much

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