A ball of mass $0.1\, Kg$. is whirled in a horizontal circle of radius $1\, m$. by means of a string at an initial speed of $10\, R.P.M.$ Keeping the radius constant, the tension in the string is reduced to one quarter of its initial value. The new speed is ....... $r.p.m.$
A$5$
B$10$
C$20$
D$14$
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A$5$
a (a) $T = m{\omega ^2}r$ $⇒$ $\omega \propto \sqrt T $
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In figure, two blocks are separated by a uniform strut attached to each block with frictionless pins. Block $A$ weighs $400\,N$, block $B$ weighs $300\,N$, and the strut $A B$ weigh $200\,N$. If $\mu=0.25$ under $B$, determine the minimum coefficient of friction under $A$ to prevent motion.
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