If the distance between object and its two times magnified virtual image produced by a curved mirror is $$15 \mathrm{~cm}$$, the focal length of the mirror must be:

A plane electromagnetic wave of frequency $$35 \mathrm{~MHz}$$ travels in free space along the $$X$$-direction. At a particular point (in space and time) $$\vec{E}=9.6 \hat{j} \mathrm{~V} / \mathrm{m}$$. The value of magnetic field at this point is :

In an a.c. circuit, voltage and current are given by:

$$V=100 \sin (100 t) V$$ and $$I=100 \sin \left(100 t+\frac{\pi}{3}\right) \mathrm{mA}$$ respectively.

The average power dissipated in one cycle is:

A particle is moving in a straight line. The variation of position '$$x$$' as a function of time '$$t$$' is given as $$x=\left(t^3-6 t^2+20 t+15\right) m$$. The velocity of the body when its acceleration becomes zero is :