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A football (soccer ball) of radius R is kept on a hole of radius r (r les than R) made on a plank kept horizontally. One end of the plank is now lifted so that it gets tilted making an angle theta from the horizontal. The maximum value of theta so that the ball does not start rolling satisfies:
a) sin(theta)=r/R
b) tan(theta)=r/R
c) sin(theta)=r/2R
d) tan(theta)=r/2R

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