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8.E: Fixed-Axis Rotation Introduction (Exercises)

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    10.2 Rotation with Constant Angular Acceleration

    1. What hanging mass must be placed on the cord to keep the pulley from rotating (see the following figure)? The mass on the frictionless plane is 5.0 kg. The inner radius of the pulley is 20 cm and the outer radius is 30 cm.

    Figure shows the pulley in which a mass of 5 kg rests on an inclined plane at a 45 degree angle and acts as a counterweight to an object of the unknown mass that hangs in the air.

    1. Calculate the torque about the z-axis that is out of the page at the origin in the following figure, given that F1 = 3 N, F2 = 2 N, F3 = 3 N, F4 = 1.8 N.

    Figure shows the XY coordinate system. Force F1 is applied from the point that is located at the line that originates from the center of the coordinate system and is directed towards the top right corner. Point is 3 meters away from the origin and force F1 is directed towards the right bottom corner. Force F2 is applied from the point that is located at the Y axis, 2 meters above the center of the coordinate system. Force F2 forms 30 degree angle with the line parallel to the X axis and is directed towards the left bottom corner. Force F3 is applied from the center of coordinate system and is directed towards the left bottom corner. Force F4 is applied from the point that is located at the X axis, 2 meters to the right from the center of the coordinate system. Force F2 forms 20 degree angle with the line parallel to the Y axis and is directed towards the left bottom corner.

    1. A seesaw has length 10.0 m and uniform mass 10.0 kg and is resting at an angle of 30° with respect to the ground (see the following figure). The pivot is located at 6.0 m. What magnitude of force needs to be applied perpendicular to the seesaw at the raised end so as to allow the seesaw to barely start to rotate?

    Figure shows a seesaw. One of the ends of the seesaw rests on the ground forming 30 degree angle with it, another end is hanging in the air.

    1. A torque of 5.00 x 103 N • m is required to raise a drawbridge (see the following figure). What is the tension necessary to produce this torque? Would it be easier to raise the drawbridge if the angle \(\theta\) were larger or smaller?

    Figure shows the drawbridge that has a length of 6 meters. A force is applied at a 30 degree angle towards the drawbridge.

    1. A horizontal beam of length 3 m and mass 2.0 kg has a mass of 1.0 kg and width 0.2 m sitting at the end of the beam (see the following figure). What is the torque of the system about the support at the wall?

    Figure shows a horizontal beam that is connected to the wall. Beam has a length of 3 m and mass 2.0 kg. In addition, a mass of 1.0 kg and width 0.2 m sits at the end of the beam.

    1. What force must be applied to end of a rod along the x-axis of length 2.0 m in order to produce a torque on the rod about the origin of 8.0\(\hat{k}\) N • m?
    2. What is the torque about the origin of the force (5.0 \(\hat{i}\) − 2.0 \(\hat{j}\) + 1.0\(\hat{k}\)) N if it is applied at the point whose position is: \(\vec{r}\) = (−2.0 \(\hat{i}\) + 4.0\(\hat{j}\)) m?

    A uniform rod of length L and mass M is held vertically with one end resting on the floor as shown below. When the rod is released, it rotates around its lower end until it hits the floor. Assuming the lower end of the rod does not slip, what is the linear velocity of the upper end when it hits the floor?

    Contributors and Attributions

    Samuel J. Ling (Truman State University), Jeff Sanny (Loyola Marymount University), and Bill Moebs with many contributing authors. This work is licensed by OpenStax University Physics under a Creative Commons Attribution License (by 4.0).

    This page titled 8.E: Fixed-Axis Rotation Introduction (Exercises) is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by OpenStax via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.