TUGAS UAS

Nama : Rahmi Hartinah
NIM : RSA1C311014
Pend. Fisika PGSBI 2011

1. ) Kinetic energy is energy owned by any object when it is moving. For example, people running, a car running in medium speed, rotating object, moving cart, and billiard. When moving, objects have energy. Because kinetic energy is owned by moving object, the value of energy is depended on mass and velocity.

In my report is about billiard. In billiard, we often see a ball hit using stick will move and hit the other ball. What happens with the ball? In fact, the ball also moves because of the motion of the first ball. This means that moving ball is able to do work or has energy. The energy is called kinetic energy. Value kinetic energy of any object is depending on it mass and speed. The formula is :

Ek = _½ mv²

Ek : Kinetic Energy (Joule)

m : mass of oject (kg)

v : velocity of any object (m/s)

For example :

An object has 70 kg of mass and is moving with 6 m/s of speed. Calculate the kinetic energy.

Solution:

Known : m = 70 kg

               V = 6 m/s

Question : Ek = ….. ?

Answer : Ek = _½ mv²

                               ⁼  _{½ x 70kg} x (6 m/s)²

                       = 1260 Joule

Thus, the kinetic energy of the object is 1260 Joule.

Based on the example above, it was concluode that to perform its work, energy is needed. Until nowadays, there is no instrument that can produce energy without deriving energy from outside. This means, energy can not be created, only altered to the other form of energy. The statement above is known as conservation laws of energy.

2 ) Look at the experiment about Pendulum..

Ok, let see…

1.      Prepare all the material (such as a pendulum with weight of 100 grams, thread about 150 cm, a prop, a stopwatch)

2.      Tie the pendulum with the thread and hang it on the prop

3.      Swing the pendulum with oscillation deviation (amplitude) of 10⁰  

4.      Write the time of 10 oscillations. How long does it take ?

5.      Repeat the experiment by changing the amplitude (not more than 15⁰   )

For the experiment, we get the concluded as follow, even if the amplitudes are different, it turns out that 10 times oscillations need the same amount of time, the time needed to do one oscillation (period) of different amplitudes turns out to be the same.

So, the time of a period does not depend on the amplitude but on the number of oscillations in one unit of time.

3 )Electricity is the flow electrons from atom to atom in a conductor. All atoms have a particles call electrons located in orbit around a proton.

Ohm’s law is “ the amount of current strength (I) through a conductor between two points is proportional to the potential difference or voltage (V) at two points, and inversely to the resistance (R)”.

The formula electricity is :

I = V / R

The problem:

In the one battery, the voltage is 1,5 V. and connected to electricity with the current is 15 A.

How much the value for Resistance?

Solution :

Know : V = 1,5 V

               I = 15 A

Question : R = ……?

Answer : I = V / R

So,                   15 A = 1,5 V / R

                        R = 1,5 V / 15A

                        R = 0.1 Ohm

 4 )

Sound as a wave

In our daily life, we always produce sounds. Musical sound, motorize vehicle sound, or the sound your produce when communicating with other person are examples of sounds. There are loud hear able sounds, there are also weak hear able sounds, and nice to listen hear able sounds. Because human hearing is limited, there are sounds we can hear and there are also sounds we cannot hear.

Sound has characteristic, such as it originated from an oscillating object, it propagates through air in the form of a longitudinal wave, it need a medium to propagate, and it reflects if it hits a barrier wall. So, as a mechanic wave, sound can only propagate through a medium.

Sound can be heard if there are three factors, which are sound source, medium, and listener. Sound source is anything that can produce sound. Loudness of sound depends on amplitude, oscillation, and distance from sound source to the listener.

The sound wav can be heard if there is a medium for propagating from the source to the listener. The sound you hear is usually from a source which propagates through air. In vacuum space, sound wave cannot propagate so the sound produce cannot be heard.

So, the conclude is sound is a result of an oscillating object and sound is wave depended to sound source, medium, and listener. If there is no medium, we cannot hear a sound.