The spring extends by x on loading, then energy stored by the spring is (if T is the tension in spring and k is
spring constant

• $\frac{{\mathrm{T}}^2}{2\mathrm{k}}$

• $\frac{{\mathrm{T}}^2}{2{\mathrm{k}}^2}$

• $\frac{2k}{{\mathrm{T}}^2}$

• $\frac{2{\mathrm{T}}^2}{k}$

A cylinder contains 10kg of gas at pressure of 10⁷ N/m². The quantity of gas taken out of the cylinder, if final pressure is 2.5×10⁶ N/m² will be( temperature of gas is constant)

• 15.2 kg

• 3.7 kg

• zero

• 7.5 kg

A resonance air column of length 40 cm resonates with tunning fork of frequency 450Hz. Ignoring end corrections , the velocity of sound in air will be

• 1020m/s

• 920m/s

• 820m/s

• 720m/s

If vibration of string is to be two times, then tension in the string must be made

• Eight times

• Four times

• Twice

• Half

A siren emitting sound of frequency 500 Hz is going away from a stationary listener with a speed of 50 m/s, the frequency of sound heard directly from the siren is 

• 286.5 HZ

• 481 Hz

• 434.2 Hz

• 580 Hz

The kinetic energy of one molecule of a gas at normal temperature and pressure will be (k = 8.31 J/mole K)

• 1.7×10³ J

• 10.2×10³ J

• 3.4×10³ J

• 6.8×10³ J

A charged particle is suspended equillibrium in a uniform vertical electric field of intensity 2000V/m. If mass of the particle is 9.6×10^-16 kg, the charge on it and excess number of electrons on the particle respectively are (g=10m/s²)

• 4.8×10^-19 C,3

• 5.8×10^-19 C,4

• 3.8×10^-19C, 2

• 2.8×10^-19 C, 1

A transmitting station transmits radiowaves of wavelength 360 m. Calculate the inductance of coil required with a condenser of capacity 1.20 μF in the resonant circuit to receive them

• 3.07×10^-8 H

• 2.07×10^-8 H

• 4.07×10^-8 H

• 6.07×10^-8 H

A circular coil of mean radius of 7 cm and having 4000 turns is rotated at the rate of 1800 revolutions per minute in the earth's magnetic field (B=0.5 gauss), the emf induced in coil will be

• 1.158 V

• 0.58 V

• 0.29 V

• 5.8 V

20.

The peak value of alternating current is $5\sqrt{2}$ ampere. The mean square value of current will be

• 5 A

• 2.5 A

• $5\sqrt{2}$ A

• None of the above