O Level Physics Question

SiYuan · 17th September 2008, 18:41

1. The problem statement, all variables and given/known data
A light spring balance is attached to two strings that passes over smooth pulleys. Loads of m1 and m2 are attached to the ends of the strings. If m1=m2=4.0kg, or m1=6kg m2=4kg, what is the reading of the spring balance.

Ans: 40N and 48N

I just need to know how do i do it. And a general theory behind it all. Sorry for this very simple question here.

It's basically like this

o------Spring-----o
|```````````````|
m1``````````````m2

Cheers for the upcoming help.

I know it's very easy. But i'm really bad at physics and such.

SiYuan · 17th September 2008, 18:47

C'mon it's 1:47am and cold like hell.

Ecroyd · 17th September 2008, 18:55

hehe thats really easy

SiYuan · 17th September 2008, 18:56

I need to know how to do it.

SiYuan · 17th September 2008, 19:01

Come on!

33 views and no one steps up to answer?

samabachan · 17th September 2008, 19:03

Try resolving horizontally then vertically then find the hypotenuse then pop.

prateik · 17th September 2008, 19:06

it should be 4N and 4.8N

havent done it for a while .. not sure
the reading will be the tension in the string

basic eq : m1g-T=m1a [newtons second law]
in the first case .. masses equal .. a == 0

hence solving for T == m1g or 4g or 4N

second case

4g-T= 4(-a) (-ve acceleration)
6g-T=6a

solving for T
24g = 5T
t= 24/5g = 4.8g or 4.8N

1871_Biscuit · 17th September 2008, 19:07

Pi²

Easy! Next.

SiYuan · 17th September 2008, 19:07

G's actually 10ms here on Earth.

samabachan · 17th September 2008, 19:08

Quote:

Originally Posted by prateik

it should be 4N and 4.8N

havent done it for a while .. not sure
the reading will be the tension in the string

basic eq : m1g-T=m1a [newtons second law]
in the first case .. masses equal .. a == 0

hence solving for T == m1g or 4g or 4N

second case

4g-T= 4(-a) (-ve acceleration)
6g-T=6a

solving for T
24g = 5T
t= 24/5g = 4.8g or 4.8N

g=9.81 (or 10 if you like). Also isn't the thing at rest so how can it have an acceleration?

prateik · 17th September 2008, 19:09

right ..was told its 9.8 unless its in the question to assume it as 10

so 40N and 48N ..

i just removed the g instead of taking it as 10

SiYuan · 17th September 2008, 19:10

Quote:

Originally Posted by prateik

it should be 4N and 4.8N

havent done it for a while .. not sure
the reading will be the tension in the string

basic eq : m1g-T=m1a [newtons second law]
in the first case .. masses equal .. a == 0

hence solving for T == m1g or 4g or 4N

second case

4g-T= 4(-a) (-ve acceleration)
6g-T=6a

solving for T
24g = 5T
t= 24/5g = 4.8g or 4.8N

So resultant force always Weight x g -T ?

And the spring reading is always Tension?

samabachan · 17th September 2008, 19:12

Quote:

Originally Posted by SiYuan

So resultant force always MASS x g -T ?

And the spring reading is always Tension?

Fixed. You'd get slaughtered by nerdy physics teachers for writing weight.

poisson · 17th September 2008, 19:14

its all just a load of bollocks.

spring, tension, upthurst, centripetal force, FUCK OFF

SiYuan · 17th September 2008, 19:18

Quote:

Originally Posted by poisson

its all just a load of bollocks.

spring, tension, upthurst, centripetal force, FUCK OFF

So it's just -F then?

prateik · 17th September 2008, 19:19

the spring reading will show the tension in the string

newtons law = downward force = upward force

so mass x g + mass x downward acc (downward force) = tension inthe string

== mass x g - T = mass x (upward acc)
the acceleration can be - or + depending on the direction the object moves

the acc for the 4kg mass would be considered positive and the 6kg one negative (did the opposite in the solution) .. the answer will remain the same

Psmith · 17th September 2008, 19:19

The answer is 42.

poisson · 17th September 2008, 19:20

Quote:

Originally Posted by SiYuan

So it's just -F then?

yes

poisson · 17th September 2008, 19:24

F = MA

A = (V - U)/T
where v = final velocity and u = initial velocity

so,

F = M x (V-U)/T

F = MV - MU / T

FT = MV - MU

now, what the fuck is FT??

SiYuan · 17th September 2008, 19:29

force x time

poisson · 17th September 2008, 19:30

Quote:

Originally Posted by SiYuan

force x time

interesting

Alex · 17th September 2008, 19:40

How are you having trouble with that problem, it's easy

17th September 2008, 18:41	#1 (permalink)
SiYuan Cafe Grandmaster 2008 Join Date: Oct 2005 Location: Where Crouch is a Midget. Posts: 6,899	O Level Physics Question 1. The problem statement, all variables and given/known data A light spring balance is attached to two strings that passes over smooth pulleys. Loads of m1 and m2 are attached to the ends of the strings. If m1=m2=4.0kg, or m1=6kg m2=4kg, what is the reading of the spring balance. Ans: 40N and 48N I just need to know how do i do it. And a general theory behind it all. Sorry for this very simple question here. It's basically like this o------Spring-----o \|```````````````\| m1``````````````m2 Cheers for the upcoming help. I know it's very easy. But i'm really bad at physics and such.

17th September 2008, 18:47	#2 (permalink)
SiYuan Cafe Grandmaster 2008 Join Date: Oct 2005 Location: Where Crouch is a Midget. Posts: 6,899	C'mon it's 1:47am and cold like hell.

17th September 2008, 18:55	#3 (permalink)
Ecroyd Strangely aroused by Lizard King Join Date: Dec 2007 Location: next door Posts: 2,387	hehe thats really easy

17th September 2008, 18:56	#4 (permalink)
SiYuan Cafe Grandmaster 2008 Join Date: Oct 2005 Location: Where Crouch is a Midget. Posts: 6,899	I need to know how to do it.

17th September 2008, 19:01	#5 (permalink)
SiYuan Cafe Grandmaster 2008 Join Date: Oct 2005 Location: Where Crouch is a Midget. Posts: 6,899	Come on! 33 views and no one steps up to answer?

17th September 2008, 19:03	#6 (permalink)
samabachan Cockface McSticklebrick Join Date: Jul 2006 Location: He plays on the left, he plays on the riiiiiiiight, our boy Ronaldo made you look shite. Posts: 4,248	Try resolving horizontally then vertically then find the hypotenuse then pop.

17th September 2008, 19:06	#7 (permalink)
prateik Reserve Team Player Join Date: Dec 2005 Posts: 3,050	it should be 4N and 4.8N havent done it for a while .. not sure the reading will be the tension in the string basic eq : m1g-T=m1a [newtons second law] in the first case .. masses equal .. a == 0 hence solving for T == m1g or 4g or 4N second case 4g-T= 4(-a) (-ve acceleration) 6g-T=6a solving for T 24g = 5T t= 24/5g = 4.8g or 4.8N

17th September 2008, 19:07	#8 (permalink)
1871_Biscuit Cock Join Date: Aug 2007 Location: Reading, Berkshire Viva Los Hombres de Galleta! Urzzz Posts: 7,223	Pi² Easy! Next.

17th September 2008, 19:07	#9 (permalink)
SiYuan Cafe Grandmaster 2008 Join Date: Oct 2005 Location: Where Crouch is a Midget. Posts: 6,899	G's actually 10ms here on Earth.

17th September 2008, 19:09	#11 (permalink)
prateik Reserve Team Player Join Date: Dec 2005 Posts: 3,050	right ..was told its 9.8 unless its in the question to assume it as 10 so 40N and 48N .. i just removed the g instead of taking it as 10

17th September 2008, 19:14	#14 (permalink)
poisson running through your veins Join Date: Feb 2005 Location: in a pond Posts: 3,830	its all just a load of bollocks. spring, tension, upthurst, centripetal force, FUCK OFF

17th September 2008, 19:19	#16 (permalink)
prateik Reserve Team Player Join Date: Dec 2005 Posts: 3,050	the spring reading will show the tension in the string newtons law = downward force = upward force so mass x g + mass x downward acc (downward force) = tension inthe string == mass x g - T = mass x (upward acc) the acceleration can be - or + depending on the direction the object moves the acc for the 4kg mass would be considered positive and the 6kg one negative (did the opposite in the solution) .. the answer will remain the same

17th September 2008, 19:19	#17 (permalink)
Psmith First Team Sub Join Date: May 2006 Location: All that is necessary for stupidity to triumph on the Caf is for good posters to do nothing Posts: 6,659	The answer is 42.

17th September 2008, 19:24	#19 (permalink)
poisson running through your veins Join Date: Feb 2005 Location: in a pond Posts: 3,830	F = MA A = (V - U)/T where v = final velocity and u = initial velocity so, F = M x (V-U)/T F = MV - MU / T FT = MV - MU now, what the fuck is FT??

17th September 2008, 19:29	#20 (permalink)
SiYuan Cafe Grandmaster 2008 Join Date: Oct 2005 Location: Where Crouch is a Midget. Posts: 6,899	force x time

17th September 2008, 19:40	#22 (permalink)
Alex Spam Alert! Join Date: Aug 2007 Location: Californication Posts: 21,224	How are you having trouble with that problem, it's easy