Question

What is the change in kinetic energy of a
body initially moving with 8m/s & finally
moving with 12m/second if the mass of the
body is 800g?​

Answer 1

Given :-

▪ Initial velocity of the body, u = 8 m/s

▪ Final velocity of the body, v = 12 m/s

▪ Mass of the body is, m = 800 g or 0.8 kg

To Find :-

▪ Change in Kinetic energy.

Solution :-

The kinetic energy of a body of mass m and travelling with velocity v is given as:

⇒ K.E = 1/2 × mv²

Here, We have final and initial velocities of the body. We will find the kinetic energy in both the cases and subtract them to get the change in Kinetic energy.

Case 1 : ( v = 8 m/s )

In this case,

⇒ K.E = 1/2 × 0.8 × 8²

⇒ K.E = 32 × 0.8

⇒ K.E = 25.6 J ...(1)

Case 2 : ( v = 12 m/s )

Similarly,

⇒ K.E = 1/2 × 0.8 × 12²

⇒ K.E = 72 × 0.8

⇒ K.E = 57.6 J ...(2)

Now,

⇒ Change in K.E = (2) - (1)

⇒ Change in K.E = 57.6 - 25.6

⇒ Change in K.E = 32 J

Hence, The change in Kinetic energy of the body is 32 joules.

Answer 2

$\bf{\gray{\underbrace{\blue{GIVEN:-}}}}$

• A body initial moving with a velocity of 8 m/s .

• Finally the body was moving with a velocity of 12 m/s .

• The mass of the body is 800g or 0.8 kg .

$\bf{\gray{\underbrace{\blue{TO\:FIND:-}}}}$

• The change in Kinetic energy .

$\bf{\gray{\underbrace{\blue{SOLUTION:-}}}}$

$\green\bigstar\:\bf{\gray{\overbrace{\underbrace{\purple{K.E\:=\:\dfrac{1}{2}\:mv^2\:}}}}}$

Where,

• $\bf\red{m}$ = mass

• $\bf\red{v}$ = Velocity

Initial kinetic energy :-

$\rm{:\implies\:K.E_i\:=\:\dfrac{1}{2}\times{0.8}\times{8^2}\:}$

$\bf\green{:\implies\:K.E_i\:=\:25.6\:J\:}$

Final kinetic energy :-

$\rm{:\implies\:K.E_f\:=\:\dfrac{1}{2}\times{0.8}\times{(12)^2}\:}$

$\bf\green{:\implies\:K.E_f\:=\:57.6\:J\:}$

$\red\checkmark\:\bf\blue{Change\:in\:K.E\:=\:K.E_f\:-\:K.E_i\:}$

➳ Change in K.E = (57.6 - 25.6) J

➳ Change in K.E = 32 J

$\red\therefore$ The change in Kinetic energy is "32 J" .