# Dinamika Rotasi

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• 1.

### Roda berbentuk cincin memiliki massa 8 kg dengan momen inersia 0,5 kg.m2. Maka jari-jari girasi roda tersebut terhadap porosnya adalah………….

• A.

25 m

• B.

20 m

• C.

16 m

• D.

2 m

• E.

0.25 m

E. 0.25 m
Explanation
The given question asks for the radius of gyration of a ring-shaped wheel. The radius of gyration is a measure of how the mass of an object is distributed from its axis of rotation. It is calculated by taking the square root of the ratio of the moment of inertia to the mass of the object. In this case, the moment of inertia is given as 0.5 kg.m2 and the mass is given as 8 kg. By plugging these values into the formula, we can calculate the radius of gyration as 0.25 m.

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• 2.

### Sebuah bola pejal bermassa 0,25 kg dan jari-jari 20 cm, diputar pada sumbu yang melalui pusat bola dengan kecepatan sudut 750 rpm. Momentum sudut bola adalah….……….kg m2/s

• A.

0.05 p

• B.

0.10 p

• C.

0.20 p

• D.

0.25 p

• E.

0.63 p

B. 0.10 p
Explanation
The momentum of an object can be calculated using the formula: momentum = mass * velocity. In this case, the momentum of the solid ball can be calculated using the formula: momentum = moment of inertia * angular velocity. The moment of inertia of a solid ball rotating about its center is given by the formula: moment of inertia = (2/5) * mass * radius^2. Plugging in the given values, we can calculate the moment of inertia. Then, multiplying the moment of inertia by the given angular velocity, we can find the momentum of the ball. The correct answer, 0.10 p, represents the calculated momentum of the solid ball.

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• 3.

### Suatu gaya menyinggung tepi silinder pejal homogen bermassa 200 gram jari-jari 50 cm, menyebabkan silinder berrotasi dengan percepatan sudut 4 rad/s2. Momen gaya yang bekerja pada silinder adalah……….

• A.

1.6 Nm

• B.

0.625 Nm

• C.

0.2 Nm

• D.

0.1 Nm

• E.

0.025 Nm

D. 0.1 Nm
Explanation
The moment of force (torque) acting on an object can be calculated using the equation Torque = Moment of Inertia * Angular Acceleration. In this case, the moment of inertia of the solid cylinder can be calculated using the equation Moment of Inertia = (1/2) * mass * radius^2. Plugging in the given values, we get Moment of Inertia = (1/2) * 0.2 kg * (0.5 m)^2 = 0.025 kgm^2. The angular acceleration is given as 4 rad/s^2. Substituting these values into the torque equation, we get Torque = 0.025 kgm^2 * 4 rad/s^2 = 0.1 Nm. Therefore, the correct answer is 0.1 Nm.

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• 4.

### Silinder pejal menggelinding murni di atas lantai datar yang kasar dengan kecepatan tetap 4 m/s. Bila diketahui massa silinder 0,1 kg maka energi kinetiknya…….

• A.

1 J

• B.

1.2 J

• C.

2 J

• D.

2.2 J

• E.

3 J

B. 1.2 J
Explanation
The kinetic energy of an object can be calculated using the formula KE = 1/2 * m * v^2, where KE is the kinetic energy, m is the mass of the object, and v is the velocity of the object. In this case, the mass of the cylinder is given as 0.1 kg and the velocity is given as 4 m/s. Plugging these values into the formula, we get KE = 1/2 * 0.1 kg * (4 m/s)^2 = 1.2 J. Therefore, the correct answer is 1.2 J.

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• 5.

### Momen inersia sebuah benda yang berotasi terhadap titik tetap dipengaruhi oleh……..

• A.

Massa benda

• B.

Volume benda

• C.

Massa jenis benda

• D.

Percepatan sudut benda

• E.

Kecepatan sudut awal

A. Massa benda
Explanation
The moment of inertia of a rotating object is influenced by its mass. The greater the mass of the object, the greater its moment of inertia will be. This is because the moment of inertia is a measure of an object's resistance to changes in its rotation, and a higher mass means a greater resistance to changes in rotation. Therefore, the correct answer is mass of the object.

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• 6.

### Sebuah benda berotasi dengan momen inersia 2,5 x 10-3 kg.m2 dan kecepatan sudut awal 5 rad/s. Agar benda itu berhenti dalam waktu 2,5 sekon, maka besar momen gaya yang harus dikerjakan adalah……..

• A.

2,5 x 10-4 N.m

• B.

7,5 x 10-4 N.m

• C.

5,0 x 10-3 N.m

• D.

7,5 x 10-3 N.m

• E.

2,5 x 10-2 N.m

C. 5,0 x 10-3 N.m
Explanation
The moment of inertia of an object is a measure of its resistance to changes in rotational motion. In this question, the moment of inertia is given as 2.5 x 10-3 kg.m2. The initial angular velocity is given as 5 rad/s. To bring the object to a stop in 2.5 seconds, a torque must be applied. The torque is calculated using the equation torque = moment of inertia x angular acceleration. Since the object is brought to a stop, the final angular velocity is 0 rad/s. Using the equation final angular velocity = initial angular velocity + (angular acceleration x time), we can calculate the angular acceleration. Substituting the values into the torque equation, we find that the magnitude of the torque required is 5.0 x 10-3 N.m.

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• 7.

### Sebuah silinder memiliki momen inersia 2 kg.m2 dalam keadaan diam, kemudian diberi gaya sehingga setelah 2 sekon kecepatan sudutnya menjadi 10 rad.s-2. Besar momen gaya yang bekerja pada silinder itu adalah……….

• A.

10 Nm

• B.

5 Nm

• C.

3 Nm

• D.

2 Nm

• E.

1 Nm

A. 10 Nm
Explanation
The moment of inertia (I) of a cylinder is given as 2 kg.m2. The equation for torque (τ) is τ = Iα, where α is the angular acceleration. The question states that the angular acceleration is 10 rad.s-2. Plugging in the values, we get τ = 2 kg.m2 * 10 rad.s-2 = 20 Nm. Therefore, the correct answer is 20 Nm.

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• 8.

### Empat buah benda massanya sama 4 terletak pada titik-titik sudut bujur sangkar yang sisi-sisinya 20 cm dan massa rusuk dapat diabaikan. Besar momen inersia system, jika sistem di putar dengan poros melalui salah satu diagonalnya adalah……

• A.

0,08 kg.m2

• B.

0,16 kg.m2

• C.

0,32 kg.m2

• D.

0,48 kg.m2

• E.

0,64 kg.m2

B. 0,16 kg.m2
Explanation
The moment of inertia of a system can be calculated by summing up the moments of inertia of each individual object in the system. In this case, we have four objects with the same mass located at the corners of a square with sides of 20 cm. Since the masses are located at the corners, we can consider them as point masses. The moment of inertia of a point mass rotating about an axis passing through its center is given by I = m*r^2, where m is the mass and r is the distance from the axis of rotation. In this case, the distance from each mass to the axis of rotation (the diagonal of the square) is half of the length of the diagonal, which is 10 cm. Therefore, the moment of inertia for each mass is 0.08 kg.m^2. Since there are four masses, the total moment of inertia for the system is 4 times that value, which is 0.32 kg.m^2.

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• 9.

### Batu gerinda berjari-jari 6 cm berputar pada porosnya sehingga menghasilkan momen inersia 2,7 x 10-3 kg.m2. Massa batu gerinda tersebut adalah…………..

• A.

0,75 kg

• B.

1,13 kg

• C.

1,50 kg

• D.

1,75 kg

• E.

2,25 kg

A. 0,75 kg
Explanation
The moment of inertia of an object is directly proportional to its mass. In this case, the moment of inertia is given as 2.7 x 10^-3 kg.m^2. Since the moment of inertia is directly proportional to the mass, a smaller moment of inertia implies a smaller mass. Therefore, the correct answer is 0.75 kg, as it is the smallest mass listed.

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• 10.

### Piringan gerinda sedang berputar horizontal dengan sumbu vertikal pada titik pusatnya.Jika segumpal plastisin dijatuhkan pada tepi piringan, maka akan terjadi…..

• A.

Kecepatan sudut naik karena momen inersianya bertambah

• B.

Kecepatan sudutnya turun karena momen inersianya bertambah

• C.

Kecepatan sudutnya tetap karena momen inersianya bertambah

• D.

Kecepatan sudutnya turun karena momen inersianya berkurang

• E.

Kecepatan sudutnya tetap