# List of physics formulas class 11 chapter Centre of Mass for CBSE ,IIT JEE & NEET

## Rigid body

A body which does not under go deformation when it is subjected to an external force is called rigid body.

### Non Rigid body

A body which undergoes deformation when subjected to an external force is called non rigid body.

### A body can execute 3 types of motions

• translatory motion
• rotatory motion
• vibratory motion

Translatory motion: A body in which all the particles same displacement in same time is called translatory motion.

Rotatory motion: A body in which the particles move permanently around a fixed point point the the motion of the body is called rotatory motion.

### Centre of mass

Centre of mass is a point with in the boundaries of a system or a body at which its entire mass appears to be concentrated.

When two particles of masses m1 and m2 are located on a straight line, their centre of mass lies on the line joining the two particles.

Let r1 and r2 be the distance of the particles from their centre of mass respectively, then

m1r1 = m2r2

### Coordinates of centre of mass

Let us consider a system of n particles of masses m1, m2, . ……. mn whose co-ordinates are (x1, y1, z1) (x2, y2, z2), …….. , (xn, yn, zn) respectively. Then co-ordinates of their centre of mass are

### Position vector of centre of mass

Consider two particles of mass m1 and m2 whose position are represented by position vectors r1 and r2 respectively at an instant, then

### Formula of Centre of Mass

• A system of two -point masses m1r1 = m2r2. The center of mass lies closer to the heavier mass.
• Triangle (at the centroid) yc=h/3.
• A semi-circular disc. yc= 4r/3π
• Semi-circular ring. yc= 2r/π
• Hemispherical shell. yc= r/2.
• Solid Hemisphere. yc =3r/8.

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