Moment of a rod of varying thickness

[lordsnowbrood]

Homework Statement

Q A cylindrical steel shaft of radius 2cm and long is turned upside down on a lathe to one half its radius for a distance of 20cm from one end find the distance of its centre of gravity from the thicker end.?

Homework Equations

The Attempt at a Solution

 

[lordsnowbrood]

Homework Statement

Q A cylindrical steel shaft of radius 2cm and long is turned upside down on a lathe to one half its radius for a distance of 20cm from one end find the distance of its centre of gravity from the thicker end.?

Homework Equations

anticlockwise moment=clockwise moment

The Attempt at a Solution

i don't get the question so can anyone help solve this

 

[emailanmol]

Hey,
Welcome to PF.

In the second line, is there a typing mistake?

I think you have not copied the question in its exact language , which is causing some confusion (especially the grammer.)

Can you retype it?

 

[tiny-tim]

welcome to pf!

hi lordsnowbrood! welcome to pf!

Q A cylindrical steel shaft of radius 2cm and long is turned upside down on a lathe to one half its radius for a distance of 20cm from one end find the distance of its centre of gravity from the thicker end.?

(you missed out the length … let's call it L )

do you mean that it has radius 2 cm for length L - 20 cm, and radius 1 cm for length 20 cm ?

if so, find the mass of each part, pretend it's concentrated at the centre of mass (of that part), and then use the usual formula for two masses

 

[lordsnowbrood]

hi lordsnowbrood! welcome to pf!


(you missed out the length … let's call it L )

do you mean that it has radius 2 cm for length L - 20 cm, and radius 1 cm for length 20 cm ?

if so, find the mass of each part, pretend it's concentrated at the centre of mass (of that part), and then use the usual formula for two masses

yes you are right.. but how to find mass??

 

[lordsnowbrood]

Hey,
Welcome to PF.

In the second line, is there a typing mistake?

I think you have not copied the question in its exact language , which is causing some confusion (especially the grammer.)

Can you retype it?

no mistakes buddy i copied it from my book Abbott physics

 

[tiny-tim]

yes u are right.. but how to find mass??

call the density "ρ" … it'll cancel out at the end

 

[gneill]

no mistakes buddy i copied it from my book Abbott physics

Wow! That must be Physics by Abbott and Costello then

 

[technician]

I think you have not copied the question in its exact language , which is causing some confusion (especially the grammer.)
Can you retype it?
GRAMMAR

 

[lordsnowbrood]

Homework Statement

Q A cylindrical steel shaft of radius 2cm and 50cm long is turned upside down on a lathe to one half its radius for a distance of 20cm from one end find the distance of its centre of gravity from the thicker end.?

Homework Equations

The Attempt at a Solution

i have made the changes can anyone now solve it

 

[lordsnowbrood]

Wow! That must be Physics by Abbott and Costello then

well it is a blue book published by heinemann and the author is abbott only

 

[tiny-tim]

hi lordsnowbrood!

i have made the changes can anyone now solve it

yes, you can solve it!

find the mass of each part, pretend it's concentrated at the centre of mass (of that part), and then use the usual formula for two masses …

show us what you get ​

 

[lordsnowbrood]

hi lordsnowbrood!


yes, you can solve it!

find the mass of each part, pretend it's concentrated at the centre of mass (of that part), and then use the usual formula for two masses …

show us what you get ​

how could i find the mass man ?? can u help me with that i can find volume but how to find mass in such question got no clue buddy

 

[tiny-tim]

how could i find the mass man ?? can u help me with that i can find volume but how to find mass …

call the density "ρ" … it'll cancel out at the end

 

[lordsnowbrood]

call the density "ρ" … it'll cancel out at the end

could u please solve it coz i cant?

 

[tiny-tim]

general strategy: write out the general formula first, then write it out again with the numbers in

(that's why the homework template has that section on Equations! )​

sooo …

i] what is the general formula for the volume of a cylinder?

ii] what are the volumes of these two cyliners?

iii] what are the positions of their centres of mass (from the end of the large cyiinder)?

iv] multiply by ρ to get the masses

v] what is the general formula of the position of the centre of mass of two masses?

vi] apply that formula (ρ will cancel)