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A uniform ball of radius r is placed on ...

A uniform ball of radius r is placed on the top of a sphere of radius R = 10 r. It is given a slight push due to which it starts rolling down the sphere without slipping. The spin angular velocity of the ball when it breaks off from the sphere is `omega=sqrt((p)/(q)((g)/(r)))`, where g is the acceleration due to gravity and p and q are the smallest integers. What is the value of `p+q`?

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To solve the problem, we will analyze the motion of a uniform ball rolling down a larger sphere. We will derive the spin angular velocity of the ball when it breaks off from the sphere. ### Step-by-Step Solution: 1. **Understanding the Setup**: - We have a uniform ball of radius \( r \) placed on top of a sphere of radius \( R = 10r \). - The ball is given a slight push and starts rolling down the sphere without slipping. 2. **Conservation of Energy**: - When the ball rolls down, it loses potential energy and gains kinetic energy. - The potential energy lost when the ball descends from height \( h \) is given by: \[ \Delta PE = mgH \] - The height \( H \) can be expressed in terms of the angle \( \theta \) as: \[ H = R - R \cos \theta = R(1 - \cos \theta) = 10r(1 - \cos \theta) \] - Thus, the potential energy lost becomes: \[ \Delta PE = mg \cdot 10r(1 - \cos \theta) \] 3. **Kinetic Energy**: - The total kinetic energy when the ball is rolling down consists of translational and rotational components: \[ KE = \frac{1}{2} mv^2 + \frac{1}{2} I \omega^2 \] - For a solid sphere, the moment of inertia \( I \) is given by: \[ I = \frac{2}{5} m r^2 \] - Using the rolling condition \( v = r \omega \), we can express \( \omega \) in terms of \( v \): \[ \omega = \frac{v}{r} \] - Substituting \( \omega \) into the kinetic energy equation gives: \[ KE = \frac{1}{2} mv^2 + \frac{1}{2} \left(\frac{2}{5} m r^2\right \left(\frac{v}{r}\right)^2 = \frac{1}{2} mv^2 + \frac{1}{5} mv^2 = \frac{7}{10} mv^2 \] 4. **Setting Up the Energy Equation**: - Equating the potential energy lost to the kinetic energy gained: \[ mg \cdot 10r(1 - \cos \theta) = \frac{7}{10} mv^2 \] - Canceling \( m \) from both sides: \[ g \cdot 10r(1 - \cos \theta) = \frac{7}{10} v^2 \] 5. **Centripetal Force Condition**: - At the point of breaking off, the normal force \( N \) becomes zero. The gravitational force component providing centripetal acceleration is: \[ mg \cos \theta = \frac{mv^2}{R} \] - Substituting \( R = 11r \): \[ mg \cos \theta = \frac{mv^2}{11r} \] - Canceling \( m \): \[ g \cos \theta = \frac{v^2}{11r} \] 6. **Substituting for \( v^2 \)**: - From the energy equation, we can express \( v^2 \): \[ v^2 = \frac{10g(1 - \cos \theta)}{7} \cdot 10r \] - Substituting this into the centripetal force equation: \[ g \cos \theta = \frac{\frac{10g(1 - \cos \theta)}{7}}{11r} \] 7. **Solving for \( \cos \theta \)**: - Rearranging gives: \[ 11g \cos \theta = \frac{10g(1 - \cos \theta)}{7} \] - Multiplying through by 7: \[ 77g \cos \theta = 10g - 10g \cos \theta \] - Combining terms: \[ 87g \cos \theta = 10g \] - Thus: \[ \cos \theta = \frac{10}{87} \] 8. **Finding \( \omega \)**: - Substitute \( \cos \theta \) back into the expression for \( v^2 \): \[ v^2 = \frac{10g(1 - \frac{10}{87})}{7} \cdot 10r \] - Simplifying gives: \[ v^2 = \frac{10g \cdot \frac{77}{87}}{7} \cdot 10r \] - Finally, substituting \( v = r \omega \): \[ r^2 \omega^2 = \frac{10g \cdot \frac{77}{87}}{7} \cdot 10r \] - Solving for \( \omega \): \[ \omega^2 = \frac{1100g}{609r} \] 9. **Identifying \( p \) and \( q \)**: - Comparing with the given form \( \omega = \sqrt{\frac{p}{q}\frac{g}{r}} \): \[ p = 1100, \quad q = 609 \] - Therefore, \( p + q = 1100 + 609 = 1709 \). ### Final Answer: The value of \( p + q \) is \( 1709 \).
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