Answer
Verified
413.4k+ views
Hint: Assume that the mass per unit area of the uniform disc is $\sigma $ therefore the mass of the uniform disc is ${\text{M = }}\sigma \pi {{\text{R}}^2}$ and the mass of the small disc is $\sigma \pi {\left( {\dfrac{{\text{R}}}{2}} \right)^2} = \dfrac{{\sigma \pi {{\text{R}}^2}}}{4} = \dfrac{{\text{M}}}{4}$
Formula used:
${\text{x = }}\dfrac{{\left( {{{\text{m}}_1}{{\text{r}}_1}{\text{ + }}{{\text{m}}_2}{{\text{r}}_2}} \right)}}{{\left( {{{\text{m}}_1}{\text{ + }}{{\text{m}}_2}} \right)}}$
where ${\text{x}}$ is the distance through which the centre of gravity of the remaining portion shifts
and ${{\text{m}}_1},{{\text{r}}_1}$ are the mass & radius of uniform disc and ${{\text{m}}_2},{{\text{r}}_2}$ are the mass & radius of the small disc that has been cut.
Complete step-by-step solution -
Given that,
Radius of uniform disc $ = {\text{R}}$
Radius of the smaller disc $ = \dfrac{{\text{R}}}{2}$
Let the mass per unit area of the original disc $ = \sigma $
Therefore mass of the uniform disc $ = {\text{M = }}\sigma \pi {{\text{R}}^2}$
And the mass of the small disc ${\text{ = }}\sigma \pi {\left( {\dfrac{{\text{R}}}{2}} \right)^2} = \dfrac{{\sigma \pi {{\text{R}}^2}}}{4} = \dfrac{{\text{M}}}{4}$
Now as the small disc has been cut from the uniform disc, the remaining portion is considered to be a system of two masses.
The two masses are: ${\text{M}}$ (concentrated at O) & $ - {\text{M}}$(concentrated at O')
(negative sign indicating above that the portion is removed from the uniform disc)
Let ${\text{x}}$ be the distance through which the centre of mass of the remaining portion shifts from point O.
The relation between the centre of masses of two masses is give as:
$
{\text{x = }}\dfrac{{\left( {{{\text{m}}_1}{{\text{r}}_1}{\text{ + }}{{\text{m}}_2}{{\text{r}}_2}} \right)}}{{\left( {{{\text{m}}_1}{\text{ + }}{{\text{m}}_2}} \right)}} \\
{\text{x = }}\dfrac{{\left[ {\left( {{\text{M}} \times {\text{0 - }}\dfrac{{\text{M}}}{4}} \right) \times \left( {\dfrac{{\text{R}}}{2}} \right)} \right]}}{{\left( {{\text{M - }}\dfrac{{\text{M}}}{4}} \right)}} \\
= \dfrac{{\left( {\dfrac{{ - {\text{MR}}}}{8}} \right)}}{{\left( {\dfrac{{3{\text{M}}}}{4}} \right)}} \\
= \dfrac{{ - 4{\text{R}}}}{{24}} \\
{\text{x = }}\dfrac{{ - {\text{R}}}}{6} \\
$.
Note: The relation between the centre of masses of two masses is calculated by the formula ${\text{x = }}\dfrac{{\left( {{{\text{m}}_1}{{\text{r}}_1}{\text{ + }}{{\text{m}}_2}{{\text{r}}_2}} \right)}}{{\left( {{{\text{m}}_1}{\text{ + }}{{\text{m}}_2}} \right)}}$ which is found to be $\dfrac{{ - {\text{R}}}}{6}$ here the negative sign indicates that the centre of gravity of the resulting flat body gets shifted towards the left point O.
Formula used:
${\text{x = }}\dfrac{{\left( {{{\text{m}}_1}{{\text{r}}_1}{\text{ + }}{{\text{m}}_2}{{\text{r}}_2}} \right)}}{{\left( {{{\text{m}}_1}{\text{ + }}{{\text{m}}_2}} \right)}}$
where ${\text{x}}$ is the distance through which the centre of gravity of the remaining portion shifts
and ${{\text{m}}_1},{{\text{r}}_1}$ are the mass & radius of uniform disc and ${{\text{m}}_2},{{\text{r}}_2}$ are the mass & radius of the small disc that has been cut.
Complete step-by-step solution -
Given that,
Radius of uniform disc $ = {\text{R}}$
Radius of the smaller disc $ = \dfrac{{\text{R}}}{2}$
Let the mass per unit area of the original disc $ = \sigma $
Therefore mass of the uniform disc $ = {\text{M = }}\sigma \pi {{\text{R}}^2}$
And the mass of the small disc ${\text{ = }}\sigma \pi {\left( {\dfrac{{\text{R}}}{2}} \right)^2} = \dfrac{{\sigma \pi {{\text{R}}^2}}}{4} = \dfrac{{\text{M}}}{4}$
Now as the small disc has been cut from the uniform disc, the remaining portion is considered to be a system of two masses.
The two masses are: ${\text{M}}$ (concentrated at O) & $ - {\text{M}}$(concentrated at O')
(negative sign indicating above that the portion is removed from the uniform disc)
Let ${\text{x}}$ be the distance through which the centre of mass of the remaining portion shifts from point O.
The relation between the centre of masses of two masses is give as:
$
{\text{x = }}\dfrac{{\left( {{{\text{m}}_1}{{\text{r}}_1}{\text{ + }}{{\text{m}}_2}{{\text{r}}_2}} \right)}}{{\left( {{{\text{m}}_1}{\text{ + }}{{\text{m}}_2}} \right)}} \\
{\text{x = }}\dfrac{{\left[ {\left( {{\text{M}} \times {\text{0 - }}\dfrac{{\text{M}}}{4}} \right) \times \left( {\dfrac{{\text{R}}}{2}} \right)} \right]}}{{\left( {{\text{M - }}\dfrac{{\text{M}}}{4}} \right)}} \\
= \dfrac{{\left( {\dfrac{{ - {\text{MR}}}}{8}} \right)}}{{\left( {\dfrac{{3{\text{M}}}}{4}} \right)}} \\
= \dfrac{{ - 4{\text{R}}}}{{24}} \\
{\text{x = }}\dfrac{{ - {\text{R}}}}{6} \\
$.
Note: The relation between the centre of masses of two masses is calculated by the formula ${\text{x = }}\dfrac{{\left( {{{\text{m}}_1}{{\text{r}}_1}{\text{ + }}{{\text{m}}_2}{{\text{r}}_2}} \right)}}{{\left( {{{\text{m}}_1}{\text{ + }}{{\text{m}}_2}} \right)}}$ which is found to be $\dfrac{{ - {\text{R}}}}{6}$ here the negative sign indicates that the centre of gravity of the resulting flat body gets shifted towards the left point O.
Recently Updated Pages
Basicity of sulphurous acid and sulphuric acid are
Assertion The resistivity of a semiconductor increases class 13 physics CBSE
Three beakers labelled as A B and C each containing 25 mL of water were taken A small amount of NaOH anhydrous CuSO4 and NaCl were added to the beakers A B and C respectively It was observed that there was an increase in the temperature of the solutions contained in beakers A and B whereas in case of beaker C the temperature of the solution falls Which one of the following statements isarecorrect i In beakers A and B exothermic process has occurred ii In beakers A and B endothermic process has occurred iii In beaker C exothermic process has occurred iv In beaker C endothermic process has occurred
The branch of science which deals with nature and natural class 10 physics CBSE
What is the stopping potential when the metal with class 12 physics JEE_Main
The momentum of a photon is 2 times 10 16gm cmsec Its class 12 physics JEE_Main
Trending doubts
Difference between Prokaryotic cell and Eukaryotic class 11 biology CBSE
Fill the blanks with the suitable prepositions 1 The class 9 english CBSE
Write an application to the principal requesting five class 10 english CBSE
Difference Between Plant Cell and Animal Cell
a Tabulate the differences in the characteristics of class 12 chemistry CBSE
Change the following sentences into negative and interrogative class 10 english CBSE
What organs are located on the left side of your body class 11 biology CBSE
Discuss what these phrases mean to you A a yellow wood class 9 english CBSE
List some examples of Rabi and Kharif crops class 8 biology CBSE