BackRotational Dynamics and Energy – Physics Exam Study Guidance
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Q1. A uniform cylinder has mass M = 4.0 kg, radius R = 0.060 m, and moment of inertia for rotation about an axis through its center given by . The cylinder rolls without slipping up an incline. The translational speed of the cylinder at the bottom of the incline is 4.00 m/s. What maximum height above its initial position does the cylinder reach before starting to slide back down?
Background
Topic: Conservation of Energy in Rotational Motion
This question tests your understanding of how to apply conservation of mechanical energy to a rolling object, accounting for both translational and rotational kinetic energy as it moves up an incline.
Key Terms and Formulas
Translational Kinetic Energy:
Rotational Kinetic Energy:
Moment of Inertia for Cylinder:
Relationship for Rolling Without Slipping:
Potential Energy at Height h:
Step-by-Step Guidance
Write the conservation of energy equation, equating the total kinetic energy at the bottom to the potential energy at the maximum height:
Substitute the moment of inertia for a cylinder and the rolling condition into the equation:
and
So,
Simplify the rotational kinetic energy term and combine it with the translational kinetic energy:
Total kinetic energy:
Set the total kinetic energy equal to the gravitational potential energy at height and solve for $h$:
Divide both sides by to isolate .
Try solving on your own before revealing the answer!
Final Answer: 0.61 m
Plugging in m/s and m/s gives m. The energy is shared between translational and rotational forms, so the cylinder does not reach as high as if it were sliding without rotation.
Q2. A uniform sphere has mass = 2.0 kg, radius = 0.060 m, and moment of inertia for rotation about an axis through its center given by . If it is rolling without slipping on a horizontal surface, and the translational speed of the sphere is 2.00 m/s, what is its total kinetic energy?
Background
Topic: Rotational and Translational Kinetic Energy
This question tests your ability to calculate the total kinetic energy of a rolling object, which includes both translational and rotational components.
Key Terms and Formulas
Translational Kinetic Energy:
Rotational Kinetic Energy:
Moment of Inertia for Sphere:
Rolling Without Slipping:
Step-by-Step Guidance
Calculate the translational kinetic energy using the given mass and speed:
Express the rotational kinetic energy in terms of using and :
Simplify the rotational kinetic energy expression:
Add the translational and rotational kinetic energies to get the total kinetic energy:
Try solving on your own before revealing the answer!
Final Answer: 4.0 J
Plugging in kg and m/s gives J. Both translational and rotational energies contribute to the total.