#### AFRILCATE

**WHAT IS KINETIC ENERGY?**

**Kinetic energy is the energy possessed in a body by virtue of its motion.**

**Kinetic energy is a scalar quantity which means it has magnitude but no direction.**

**WHAT IS THE FORMULAR FOR KINETIC ENERGY?**

The formula for kinetic energy is:

K.E = ^{1}/_{2 }mv^{2} |

Where,

**K.E** is the kinetic energy of the object

**m** is the mass of an object

**v** is the velocity of an object

Hence, Kinetic energy depends on mass and velocity.

**EXAMPLES OF KINETIC ENERGY**

- A river flowing at a certain speed possesses kinetic energy.
- A truck moving down the road at a certain speed has more kinetic energy than a car traveling at that same speed because the truck has more mass than the car.
- A flying plane has a very high kinetic energy not only because of its large mass but also because of its high velocity.
- Bullets from guns have high kinetic energy due to the large amount of velocity possessed by the bullet.
- When we work, run or jog, we possess some amount of kinetic energy.

**a bicycle in motion possesses kinetic energy**

**TYPES OF KINETIC ENERGY**

**Radiant Energy:**A type of kinetic energy that travels in waves through medium or space.

Examples include the Sun, the light bulb, the glowing coil on an electric cooker.

**Sound Energy:**This is energy produced by the vibration of an object. Sound energy needs a medium for its propagation and travels out in all directions. They can’t travel in a vacuum. Examples include voices and musical instruments.

**Thermal Energy:**This is also a type of**kinetic energy**that exists due to motion and collision of atoms and molecules. Example: a heated cooking spoon.**Electrical Energy:**This is energy resulting from the flow of electric charges. Examples include electric Iron, lightning.**Mechanical Energy:**This is the energy stored in objects. It is the sum of**kinetic energy**and potential energy. Example: A moving tricycle.

**WHAT IS THE UNIT OF KINETIC ENERGY?**

The standard metric unit of measurement for kinetic energy is the Joule.

1 Joule = 1 kg • m^{2}/s^{2} |

**HOW TO CALCULATE KINETIC ENERGY**

An object of mass 5kg is moving at a constant velocity of 15ms^{-1}. Calculate its K.E

__Solution__

**K.E = **^{1}**/ _{2}mv^{2}**

K.E = ^{1}/_{2} × 5 × 15^{2} = __562.5 J__

**TEST YOUR KNOWLEDGE**

1. Determine the kinetic energy of a 825-kg convertible car that is moving with a speed of 22.4 m/s.

(Tap on the option tab to reveal answer)

##### a. 3.540 Joules

**X wrong!!**

##### b. 2.07 × 10^5 Joules

**✔ Correct**

##### SHOW SOLVING

**K.E = **^{1}**/ _{2}mv^{2}**

K.E = ^{1}/_{2} × 825 × 22.4^{2}

K.E = 2.07 × 10^{5} Joules

ANS = B

2. If the convertible car in the above problem is moving with three times its speed, what would be its new kinetic energy?

##### a. 1.47 × 10^3 Joules

**X wrong!!**

##### b. 1.86 × 10 ^ 6 Joules

**✔ Correct**

##### SHOW SOLVING

**K.E = **^{1}**/ _{2}mv^{2}**

K.E = ^{1}/_{2} × 825 × (22.4 × 3)^{2}

K.E = 1.86 × 10^{6} Joules

Ans: B

## 3. Mohammed Ali, the former Africa boxing champion, had a kinetic energy of 15,000J just prior to rendering a knock-out punch to his opponent.

## If Ali’s mass is 180 kg, then what is the speed of the blow?

##### a. 16.67 m/s

**✔ Correct**

##### b. 23.18 m/s

**X wrong!!**

##### SHOW SOLVING

**K.E = **^{1}**/ _{2}mv^{2}**

15,000 = ^{1}/_{2} × 180 × v^{2}

v^{2 }=^{ }15,000 × 2 × ^{1}/_{180 }

v^{2 }= 16.67 ** ^{m}**/

_{s}ANS = A

## 4. A 900-kg propulsion jet moving at 30 m/s has 405,000 Joules of kinetic energy. Estimate its new kinetic energy if it is moving at 15m/s.

##### a. 101,250 J

**✔ Correct**

##### b. 205,700 J

**X wrong!!**

##### SHOW SOLVING

The KE is directly related to the square of the speed.

If the speed is reduced by a factor of 2 (from 30m/s to 15 m/s) then the K.E will be reduced by a factor of 4.

Thus, the new KE is (405,000 J)/4 = 101,250 J.

__Cross-Check__

**K.E = **^{1}**/ _{2}mv^{2}**

K.E = ^{1}/_{2} × 900 × (15)^{2} = 101,250 Joules

Ans: A

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