Moment of inertia equation

3 Problems and solutions about Moment of inertia equation

1. A solid cylinder has a radius of 8 cm and a mass of 2 kg. Meanwhile, a solid ball has a radius of 5 cm and a mass of 4 kg. If the two objects rotate with an axis through their center, determine the ratio of the moment of inertia of the cylinder and the ball.


Solid cylinder radius (r) = 8 cm = 0.08 m

Solid cylinder mass (m) = 2 kg

Solid ball radius (r) = 5 cm = 0.05 m

The mass of the solid ball (m) = 4 kg

Wanted: Comparison of the moment of inertia of a cylinder and a ball


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Momentum equation

3 problems and solutions about Momentum equation

1. If the object’s speed becomes 5 times its original speed, then the object’s momentum becomes ….. its original momentum.


Initial speed = v

Final speed = 5v

Mass = 1

Wanted: Momentum


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Speed equation

3 problems and solutions about the Speed equation

1. A car travels to the south for 100 m in 1 minute then turns to the east 120 m in 0.5 minutes. Determine the average speed of the car.


Total distance = 100 meters + 120 meters = 220 meters

Total time = 1 minute + 0.5 minutes = 1.5 minutes = 90 seconds

Wanted: Average speed


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Wave refraction

Articles about Wave refraction

One characteristic of waves is refraction. Refraction occurs when a wave that originally traveled through one medium enters a different medium. For example, a sound wave initially moves through the air and then encounters a wall, some sound waves are reflected by the wall, some are refracted by the wall. Refraction means that sound waves are absorbed or transmitted in the wall, but the direction of propagation changes. The change in the direction of propagation occurs because the speed of the sound wave changes when it enters a different medium from the previous medium.

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Definition formula and the types of mechanical waves

Articles about Definition formula and the types of mechanical waves


If you hold one end of the rope and vibrate it up and down, a wave appears that propagates along the rope. Or if you drop a stone into the water, waves will appear on the surface of the water. The rope and water only oscillate up and down, not moving horizontally. Waves on a rope and waves in water are examples of mechanical waves.

Mechanical waves are waves that travel through a medium. Examples of mechanical waves are waves on ropes or strings, waves in water, sound waves that propagate in the air medium, and earthquake waves that propagate in the soil medium. Waves can travel long distances while the medium through which the waves vibrate is around the equilibrium point.

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Reflection of waves

Definition of Reflection and Examples in everyday life

One characteristic of waves is experiencing reflection. Seawater waves propagate in the sea when they hit a rock then the wave reverse, so does the water wave in the water bath when it encounters a wall, the water wave reverses towards the direction it came from.

Examples of reflection experienced by sound waves are echoes and echoes. Reverberation occurs when sound is reflected while the sound source is still sounding. Usually, the echo occurs in an enclosed space. While the echo occurs when the sound is reflected after the sound source does not sound. Echo typically occurs outdoors and is not disturbing, but reverberation is frequently annoying because, for example, when someone is talking in a closed room, the reflection of the person’s voice off the walls causes the person’s speech to become blurred. To overcome this, often, on the walls of closed spaces such as auditoriums or music studios, air vibration dampers are installed that transmit sound so that sound is not reflected.

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Electric current electric charge magnetic field magnetic force

Articles about Electric current electric charge magnetic field magnetic force

In 1819, a Danish scientist named Hans Christian Oersted (1777-1851) discovered the relationship between magnetism and electric currents or moving charges. He found that when a compass needle is near a live wire, the compass needle is deflected. When there is no current, the compass needle points north.

A compass needle is a magnet, so it can be moved by a magnetic force. Where does the magnetic force (F) come from? Near the compass needle, there is a wire carrying an electric current so that the magnetic force must be exerted by the electric current.

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A dielectric is an insulator that separates the two plates or sheets of the conductor on the capacitor. Isolators are materials that cannot conduct the electric current, for example, plastic, glass, paper, or wood. The dielectric function is to increase the capacitance so that the capacitor can store more electric charge and the electric potential energy.

A capacitor can function if both conductor plates do not touch each other so that the electric charge does not move from one conductor to another. Likewise, so that the electric charge does not move from the conductor to the air, the space between the two conductors must be a vacuum. In the topic about the parallel plate, the capacitor has been discussed the capacitance of parallel plate capacitors which are separated by a vacuum. The capacitance of the capacitor in a vacuum has limitations so that to enlarge the capacitance, placed dielectric between the two plates.

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Electrical energy stored in capacitor

Article about The Electrical energy stored in capacitor

The capacitor is composed of two-conductor plates and, between the two conductors, there is a dielectric. At first, the two conductors are electrically neutral. In order for the capacitor to function, each plate or sheet of the conductor must be electrically charged, where the amount of the electric charge in each conductor is equal but different in type. Suppose that one of the charged conductors is Q = +10 Coulomb, the other conductor is Q = -10 Coulomb. The existence of the same large but opposite type of electric charge in both conductors generates an electric field between the two conductor plates, where the direction of the electric field is from the positive charge to the negative charge. In addition, there is also an electric potential difference between the two conductors, where positively charged conductors have a higher electric potential while negatively charged conductors have a lower electric potential.

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Equation of capacitor circuit

Article about The Equation of capacitor circuit

A capacitor has a certain capacitance. If the required capacitance is not available, can be connected to two or more two capacitors to obtain the required capacitance. In order to properly connected the capacitor, it needs correct knowledge about the capacitor circuit. 🙂

Equation of capacitor circuit 1Before studying the capacitor circuit, first, understand the following symbols. Two vertical lines on the capacitor symbol represent two conductors on parallel plate capacitors. In the battery symbol, a longer vertical line represents a high potential (+) and a shorter vertical line represents a low potential (-). The horizontal line of both the capacitor symbol and the battery symbol represents the cable.

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