What do athletes misuse to increase muscle strength?

$A$ hollow sphere of radius $R$ is filled completely with an ideal liquid of density $\rho$. The sphere is moving horizontally with an acceleration $2g$,where $g$ is the acceleration due to gravity. If the minimum pressure of the liquid is $P_0$,then find the pressure at the centre of the sphere.

Which of the following statements is correct?

The figure shows the cross-section of a long cylindrical conductor through which an axial hole of radius $r$ is drilled with its center at point $A$. $O$ is the center of the conductor. If an identical hole were to be drilled centered at point $B$ while maintaining the same current density,the magnitude of the magnetic field at $O$:

If $z = \sec(y - ax) + \tan(y + ax)$,then $\frac{\partial^2 z}{\partial x^2} - a^2 \frac{\partial^2 z}{\partial y^2}$ is equal to

Force acting on a particle moving in a straight line varies with the velocity of the particle as $F = \frac{K}{v}$. Here $K$ is a constant. The work done by this force in time $t$ is