A hollow spherical shell at outer radius R floats just submerged under the water surface. The inner radius of the shell is r. If the specific gravity of the shell material is $${{27} \over 8}$$ w.r.t water, the value of r is :

Assume that the displacement(s) of air is proportional to the pressure difference ($$\Delta $$p) created by a sound wave. Displacement (s) further depends on the speed of sound (v), density of air ($$\rho $$) and the frequency (f). If $$\Delta $$p ~ 10 Pa, v ~ 300 m/s, $$\rho $$ ~ 1 kg/m³ and f ~ 1000 Hz, then s will be of the order of (take the multiplicative constant to be 1) :

An electron is constrained to move along the y-axis with a speed of 0.1 c (c is the speed of light) in the presence of electromagnetic wave, whose electric field is
$$\overrightarrow E = 30\widehat j\sin \left( {1.5 \times {{10}^7}t - 5 \times {{10}^{ - 2}}x} \right)$$ V/m.
The maximum magnetic force experienced by the electron will be :
(given c = 3 $$ \times $$ 10⁸ ms^–1 and electron charge = 1.6 $$ \times $$ 10^–19 C)

A wheel is rotating freely with an angular speed $$\omega $$ on a shaft. The moment of inertia of the wheel is I and the moment of inertia of the shaft is negligible. Another wheel of moment of inertia 3I initially at rest is suddenly coupled to the same shaft. The resultant fractional loss in the kinetic energy of the system is :