Force - Centre of Gravity

Question 1

Gravitational force between two masses is always __ ? / Name an attractive force.

Answer 1

1. attractive / gravitational force

Question 2

What is the weight of a particle?

Answer 2

The force of gravity acting on a particle through which the Earth attracts it is called the weight w of the particle.

Question 3

What is weight with reference to the weight of each particle?

Answer 3

1. A body can be considered to be made up of a large no. of particles, each of which have their own different weight.
2. The force of gravity w acting on these particles can be assumed to be parallel to each other because of the body being quite small in comparison to the size of the earth.
3. All these parallel forces acting in the same direction can be replaced by a single force W of magnitude equal to the sum of all these forces.

Question 4

Define centre of gravity.

Answer 4

The centre of gravity of a body is the point about which the algebraic sum of moments of weights of all the particles constituting the body is zero. The entire weight of the body can be considered to act at this point, howsoever the body is placed.

Question 5

What does the position of centre of gravity of a body of given mass depend on?

Answer 5

It depends on the shape of the body i.e., on the distribution of mass (of particles) in it.

Question 6

When does the position of centre of gravity of a body change?

Answer 6

When the body is deformed

Question 7

Where does the centre of gravity need to be?

Answer 7

the centre of gravity doesn’t always need to be within the material of the body.

Question 8

Where does the centre of gravity of a hollow sphere or a ring lie?

Answer 8

At its centre, where there is no material

Question 9

When can a body of weight W be considered as a point particle?

Answer 9

By the concept of centre of gravity, a body of weight W can be considered as a point particle of weight W at its centre of gravity because the algebraic sum of moments of all the particles constituting the body acts as weight at a single point G.

Question 10

What is the position of the centre of gravity of a rod?

Answer 10

Mid-point of rod

Question 11

Position of the centre of gravity of a circular disc?

Answer 11

Geometric centre

Question 12

Position of CG of a solid or hollow sphere?

Answer 12

Geometric centre of the sphere

Question 13

Position of centre of gravity of a solid or hollow cylinder?

Answer 13

Mid-point on the axis of the cylinder

Question 14

Position of the centre of gravity of a solid cone?

Answer 14

At a height h/4 from the base, on its axis

Question 15

Position of the centre of gravity of a hollow cone?

Answer 15

At a height h/3 from its base, on its axis

Question 16

Position of the centre of gravity of a circular ring?

Answer 16

Centre of ring

Question 17

Position of the centre of gravity of a triangular lamina?

Answer 17

The point of intersection of medians

Question 18

Position of the centre of gravity of a parallelogram?

Answer 18

The point of intersection of diagonals

Question 19

Position of centre of gravity of a rectangular lamina?

Answer 19

The point of intersection of diagonals

Question 20

Position of the centre of gravity of a rhombus?

Answer 20

The point of intersection of diagonals

Question 21

Position of the centre of gravity of a square?

Answer 21

The point of intersection of diagonals

Question 22

How % why can a solid body be balanced?

Answer 22

On its centre of gravity, because the algebraic sum of moments of the weights of all the particles of the rule about the object doing the balancing at CG is zero

Question 23

How can we locate the centre of gravity of an irregular lamina?

Answer 23

When a body is freely suspended from a point, it comes to rest (i.e. balances) in such a position that its centre of gravity lies vertically below the point of suspension.

Question 24

Which instrument do we use to determine CG?

Answer 24

plumb line

Question 25

Where must CG be located for stable equilibrium?

Answer 25

For the stable equilibrium of the body, its CG must be as low as possible. It must be above the base and near the geometric centre of the body.