Question

If a moving ball is hit with a racket, it's velocity increases from 2 m/s to 4 m/s. If the mass of the ball in 300 g, calculate the change in kinetic energy.

Answer 1

Change in kinetic energy = 0.6 J

Explanation :

Mass of ball is 300 gram. It's velocity increases from 2 m/s to 4 m/s.

What is change in kinetic energy?

____________________________

Here,

□ Mass of ball = 300 g

□ Initial velocity = 2 m/s

□ Final velocity = 4 m/s

Now change in velocity, ∆v = 4 - 2

∴ Change in velocity = 2 m/s

Again, mass of ball = 300 g

Mass of ball = 300/1000 kg

∴ Mass of ball = 0.3 kg

We know that,

Kinetic energy (K.E.) = ½ × m × v²

⇒ K.E. = ½ × 0.3 × 2²

⇒ K.E. = ½ × 0.3 × 4

⇒ K.E. = 0.3 × 2

⇒ K.E. = 0.6 J

∴ Change in kinetic energy = 0.6 Joules.

Answer 2

Answer:

Explanation:

ANSWER:-

Given:

Initial Velocity = 2 m/s

Final Velocity = 4 m/s

Mass of Ball = 300 gms = 0.3 kg

Change in Kinetic Energy = ?

We know that :

$K.E = \frac{1}{2} mv^{2}$

Where m is mass and v is velocity.

Initial Kinetic Energy :-

K.E = $\frac{1}{2} * \frac{3}{10} * (2)^{2}$

= $\frac{3}{20} *4$

K.E = 3/5 Joules

Final Kinetic Energy :-

K.E = $\frac{1}{2} *\frac{3}{10} *(4)^2$

$= \frac{3}{20} * 16$

K.E = 12/5 Joules

Now,

Change in K.E = Final K.E - Initial K.E

Change = $\frac{12}{5} -\frac{3}{5} = \frac{9}{5}$

Change in Kinetic Energy is 9/5 Joules.

Things to Note:

• SI Unit of Kinetic Energy is Joules
• Potential Energy = mgh
• Where m is mass, g is gravity (9.8 m/s^2) and h is height

• Formula of Kinetic Energy is $\frac{1}{2} mv^2$

• Where m is mass and v is velocity.
• Change in K.E = Final K.E - Initial K.E
• Where K.E is Kinetic Energy.