Two cars A and B start from a point at the same time in a straight line and their positions are represented by $$\mathrm{R}_{\mathrm{A}}(\mathrm{t})=$$ at $$+\mathrm{bt}^2$$ and $$\mathrm{R}_{\mathrm{B}}(\mathrm{t})=x \mathrm{t}-\mathrm{t}^2$$. At what time do the cars have same velocity?

The a.c. source of e.m.f. with instantaneous value '$$e$$' is given by $$e=200 \sin (50 t)$$ volt. The r.m.s. value of current in a circuit of resistance $$50 \Omega$$ is

In the digital circuit the inputs are as shown in figure. The Boolean expression for output $$\mathrm{Y}$$ is

A double convex lens of focal length '$$F$$' is cut into two equal parts along the vertical axis. The focal length of each part will be