A solid uniform disk of mass 21.0 kg and radius 85.0 cm is at rest flat on a frictionless surface. Figure 10–76 shows a view from above. A string is wrapped around the rim of the disk and a constant force of 35.0 N is applied to the string. The string does not slip on the rim. In what direction does the cm move?
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12. Rotational Kinematics
Rolling Motion (Free Wheels)
Problem 70
Textbook Question
A bowling ball of mass 7.3 kg and radius 9.0 cm rolls without slipping down a lane at 3.7 m/s. Calculate its total kinetic energy.

1
Identify the types of kinetic energy involved: Since the bowling ball is rolling without slipping, it has both translational kinetic energy and rotational kinetic energy.
Write the formula for total kinetic energy: \( KE_{\text{total}} = KE_{\text{translational}} + KE_{\text{rotational}} \). Translational kinetic energy is given by \( KE_{\text{translational}} = \frac{1}{2} m v^2 \), and rotational kinetic energy is given by \( KE_{\text{rotational}} = \frac{1}{2} I \omega^2 \), where \( I \) is the moment of inertia and \( \omega \) is the angular velocity.
Determine the moment of inertia for a solid sphere: For a solid sphere rolling about its axis, the moment of inertia is \( I = \frac{2}{5} m r^2 \), where \( m \) is the mass and \( r \) is the radius of the sphere.
Relate angular velocity \( \omega \) to linear velocity \( v \): Since the ball rolls without slipping, \( \omega = \frac{v}{r} \). Substitute this expression for \( \omega \) into the rotational kinetic energy formula.
Substitute all known values into the total kinetic energy formula: Use \( m = 7.3 \ \text{kg} \), \( r = 0.09 \ \text{m} \), and \( v = 3.7 \ \text{m/s} \) to calculate \( KE_{\text{total}} = \frac{1}{2} m v^2 + \frac{1}{2} \left( \frac{2}{5} m r^2 \right) \left( \frac{v}{r} \right)^2 \). Simplify the expression to find the total kinetic energy.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Kinetic Energy
Kinetic energy is the energy an object possesses due to its motion, calculated using the formula KE = 1/2 mv², where m is the mass and v is the velocity. For rolling objects, both translational and rotational kinetic energy must be considered.
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Intro to Rotational Kinetic Energy
Rolling Motion
Rolling motion occurs when an object rotates about an axis while translating along a surface. For a solid sphere, the total kinetic energy is the sum of translational kinetic energy and rotational kinetic energy, which is given by KE_rotational = 1/2 Iω², where I is the moment of inertia and ω is the angular velocity.
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Conservation of Energy in Rolling Motion
Moment of Inertia
The moment of inertia is a measure of an object's resistance to changes in its rotation and depends on the mass distribution relative to the axis of rotation. For a solid sphere, the moment of inertia is I = 2/5 mR², where m is the mass and R is the radius, which is crucial for calculating the rotational kinetic energy in rolling objects.
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Intro to Moment of Inertia
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