The temperature at which oxygen molecules will have same r.m.s. speed as helium molecules at $57^{\circ} \mathrm{C}$ is (molecular masses of oxygen and helium are 32 and 4 respectively.)

A single slit diffraction pattern is formed with white light. For what wavelength of light the $4^{\text {th }}$ secondary maximum in diffraction pattern coincides with the $3^{\text {rd }}$ secondary maximum in the pattern of light of wavelength ' $\lambda$ '?

A resistor of $5 . \Omega$, inductor of self inductance $\left(\frac{2}{\pi^2}\right) \mathrm{H}$ and a capacitor of unknown capacity are connected in series to an a.c. source of $100 \mathrm{~V}, 50 \mathrm{~Hz}$ supply. When the voltage and current are in phase, the value of capacitance is

A rigid body rotates about a fixed axis with variable angular velocity $(\alpha-\beta t)$ at time $t$, where $\alpha$ and $\beta$ are constants. The angle through which it rotates before it comes to rest is