Question

(3) Define kinetic energy. OStain an expression for the kinetic energy of an object

(b) A ball of mass 400g rolls on a ground with a uniform speed of 25km/h
Find the kinetic energy possessed by it.

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Answer 1

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(a) Defination:-

The energy possessed by an object due to its motion is called as kinetic Energy.

Derivation:
Let us consider an object of mass " m " which is at rest on smooth horizontal plane.
Let a Force , F acts on the object and let the object from rest moves from point A to point B and covers a displacement S.
The WORK Done by Force on the object is :
Workdone = Force x displacement.
W= FxS ____(1).
From third equation of motion;
V^2 -U^2 =2aS
S= V^2 -U^2/2a ______(2)
By Newtons second law of motion:
F= ma
From equation 1 and 2
W= m*a* (V^2- U^2)/2a
As we have assumed object is at rest, u=0
W=m*V^2/2
The WORK Done appears as kinetic energy of the body.
Therefore,
K.E = (1/2 × mv2)

(b) Mass = 400 g = 0.4 kg

Velocity , v = 25 m/s

K.E = 1/2 ×mv²

= 1/2 ×0.4 × 25 ×25

= 125 Joules

Answer 2

a) the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity.