By Valentina Tobos | Laurentiu Tobos

Updated on Sep 28, 2011

Review these concepts at: Uniform Rotational Motion Study Guide

**Practice Questions**

- In a uniform circular motion, is the velocity constant also? Explain briefly.
- Considering the answer to practice problem 1, will there be an acceleration associated with this motion? Explain briefly.
- Is uniform circular motion a uniform linear motion also? Why?

- The angular displacement of a planet is 0.11 · 10
^{–4}degrees per second. Find the angular displacement in one Earth year. - For the previous practice problem, find the displacement in a year if the radius is 149,600 km.
- Figure 8.2 shows two different objects, at two different times, moving in a uniform circular motion. How does the angular displacement of the two objects compare?

- Calculate the period and frequency of the minute indicator on a mechanical clock.
- Calculate the tangential speed of a merry-goround of radius 6.0 m that completes a revolution in 50 s.
- Find the average tangential speed of an object at rest on the surface of Earth (the radius of the earth is 6.4 · 10
^{3}m). - A turbine engine develops 259
*rotations per minute*(rpm). Find the period of the circular motion. - In practice problem 10, find the average speed if the turbine has a radius of 1.2 m.

- Consider an object on a rotating platform. When you increase the position of the object relative to the axis of rotation, is the tangential speed or the angular speed of the object changing? Explain briefly.
- When you increase the angular speed of a rotating object, is the period increasing or decreasing?
- When you increase the angular speed of a rotating object, is the frequency increasing or decreasing?

- An Earth satellite rotates with the period of Earth. Find the angular speed and the tangential speed. Consider the distance to the satellite from the center of Earth to be 6,380 km.
- In practice problem 15, find the centripetal acceleration and the centripetal force on the satellite if the mass is 6,000 kg.
- Two objects with masses
*m*and 2 ·*m*are connected through a string and rotate in a circle together at the same distance from the center. How does the angular speed of the two objects compare, and how does the centripetal force of the two objects compare? - An object at the end of a string of length 50 cm is rotated in a uniform circular motion with 80 rpms. Find the frequency, the period of this motion, and the centripetal acceleration.
- For practice problem 18, find the centripetal force and the tension in the string at the top and the bottom of the trajectory (the object is rotated in a vertical motion). The object has a mass of 1 kg.

**Answers**

- No, direction changes.
- Yes, since acceleration is the time change of velocity.
- No, trajectory is not linear.
- 347 degrees
- 9.06 · 10
^{5}km - Equal
- 60 s and 1/60 Hz
- 7.5 · 10
^{–1}m/s - 4.7 · 10
^{–1}m/s - 2.32 · 10
^{–1}s - 32.5 m/s
*ω*stays the same and*v*is changing, increasing if the distance decreases and vice versa- Decreasing
- Increasing
- 7.27 · 10
^{–5}rad/s and 4.64 km/s - 3.4 · 10
^{8}m/s^{2}and 2 · 10^{12}N - The same angular speed. The object with larger mass has a larger centripetal force.
- 1.3 Hz, 0.75 s, 34 m/s
^{2} - 34 N, 44 N, 24 N

From Physics Success in 20 Minutes A Day. Copyright © 2006 by LearningExpress, LLC. All Rights Reserved.

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