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 mv2 |
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 • m2/s2 |
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 = 1/2mv2
K.E = 1/2 × 5 × 152 = 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 = 1/2mv2
K.E = 1/2 × 825 × 22.42
K.E = 2.07 × 105 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 = 1/2mv2
K.E = 1/2 × 825 × (22.4 × 3)2
K.E = 1.86 × 106 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 = 1/2mv2
15,000 = 1/2 × 180 × v2
v2 = 15,000 × 2 × 1/180
v2 = 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 = 1/2mv2
K.E = 1/2 × 900 × (15)2 = 101,250 Joules
Ans: A
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