Question

A uniform disc of radius 5cm is placed on another disc of radius 20 cm. Find the shift in centre of mass​

Answer 1

Let σ is mass per unit area.

Mass of disc of radius 2R is M

1

=σ×4πR

2

Mass of disc of radius R is M

2

=σ×πR

2

Centre of mass xcm=

M

1

+M

2

M

1

x

1

+M

2

x

2

⇒x

cm

=

4σπR

2

+σπR

2

4σπR

2

×0+σπR

2

×R

⇒x

cm

=

5

R

Hence, x

cm

=

5

R

right to the centre of large disc as shown in figure.