Page 300 - General Knowledge

GENERAL KNOWLEDGE 2019

 A machine is producing one watt of power if it is doing one joule of work every second. A 75-
watt light bulb uses 75 joules of energy each second.
 The standard unit used to measure power is the watt which has the symbol W.
 The unit is named after the 17th century Scottish inventor and industrialist James Watt. You
have probably come across the watt often in everyday life. The power output of electrical
equipment such as light bulbs or stereos is typically advertised in watts.
 By definition, one watt is equal to one joule of work done per second.

 So if P represents power in watts, is the change in energy and is the time taken in
seconds then:

4. ROTATIONAL MOTION AND GRAVITATION
Rotational Motion
 Rigid Body: A rigid body consists of a number of particles confined to a fixed geometrical
shape and size in such a way that the distance between any pair of particles always remains
constant.
 Moment of Inertia (Rotational Inertia): Moment of inertia of a body about a given axis is
defined as the sum of the products of the masses of different particles constituting the body
and the square of their distances from the axis of rotation.
 It depends upon two factors.
 Mass of the body

 Distribution of mass about the axis of rotation
 Moment of inertia of a body should always be referred to as a given axis, since it depends
upon distribution of mass about that axis.
 It does not depend upon the state of motion of rotating body.
 It is same whether the body is at rest, rotating slowly or rotating fast about the given axis.

∑
Rotational Kinetic Energy

So,

 Radius of Gyration: Radius of gyration of a body about a given axis is that distance, at
which if whole of the mass of the body were concentrated, it would have the same moment
of inertia as that of the body.

So, √

 Again Radius of gyration of a body about a given axis is defined as the square root of the
mean of the squares of distances of the various particles of the body from the axis of
rotation.

So, √

 Perpendicular axes theorem: It states that the moment of inertia of a plane lamina, about
an axis perpendicular to the plane lamina, is equal to the sum of the moments of inertia of
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