A stone of mass 20 g is projected from a rubber catapult of length 0.1 m and area of cross section 10^$$-$$6 m² stretched by an amount 0.04 m. The velocity of the projected stone is ______________ m/s.

(Young's modulus of rubber = 0.5 $$\times$$ 10⁹ N/m²)

In a uniform magnetic field, the magnetic needle has a magnetic moment 9.85 $$\times$$ 10^$$-$$2 A/m² and moment of inertia 5 $$\times$$ 10^$$-$$6 kg m². If it performs 10 complete oscillations in 5 seconds then the magnitude of the magnetic field is _______________ mT. [Take $$\pi$$² as 9.85]