When a string is divided into four segments of $$l_1, l_2, l_3$$ and $$l_4$$. The fundamental frequencies of these three segments are $$v_1, v_2, v_3$$ and $$v_4$$, respectively. The original fundamental frequency $$(v)$$ of the string is
A charged particle moving in a uniform magnetic field and losses $$16 \%$$ of its kinetic energy. The radius of curvature of its path changes by
A thin but rigid semicircular wire frame of radius $$r$$ is hinged at $$O$$ and can rotate in its own vertical plane. A smooth peg $$P$$ starts from $$O$$ and moves horizontally with constant speed $$2 v_0$$ lifting the frame upward as shown in figure. Find the angular velocity $$\omega$$ of the frame when its diameter makes an angle of $$60^{\circ}$$ with vertical.
After two hours one-eight of the starting amount of a certain radioactive isotope remained undecayed. The half-life of the isotope is