Apparent frequency of sound of engine is changing in the ratio 5/3 under the condition that engine is first aprroaching and then receding away from the observer. If velocity of sound is 340 m/s, then velocity of engine is

• 340 m/s

• 170 m/s

• 85 m/s

• 310 m/s

n balls each of mass m and velocity v collide with a wall, assume that the collisions are perfectly elastic. The pressure exerted per second on the wall is 

• 3 mnv

• mnv

• 2mnv

• none

13.

Eight small drops, each of equal charges and radii are coalesce to form a big drop. The capacity of bigger drop in comparison to each smaller drop will be :

• 4 times

• 2 times

• 32 times

• 8 times

An organ pipe, opened at both ends, has fundamental frequency of 30 Hz. If one of its ends is closed, then fundamental frequency will be :

• 15 Hz

• 30 Hz

• 45 Hz

• 60 Hz

A body has initial temperature of 80°C. It cools by radiation process. In 5 minutes, it cools down to 64°C and in 10 minutes, it cools down to 52$°$C. The temperature of  surrounding is:

• 8°C

• 16$°$C

• 32$°$C

• 24$°$C

The surface tension of the soap solution is T. The work done in forming a soap bubble of radius r, is :

• $8{\mathrm{\pi r}}^2\mathrm{T}$

• $4{\mathrm{\pi r}}^2\mathrm{T}$

• $\frac{4}{3}{\mathrm{\pi r}}^2\mathrm{T}$

• $\frac{8}{3}{\mathrm{\pi r}}^2\mathrm{T}$

A mixture of oxygen and hydrogen are filled in a vessel at a fixed temperature. The ratio of average kinetic energies of atoms of H₂ and O₂ is

• 1 : 16

• 1 : 8

• 1 : 12

• 1 : 1

An ice at -50°C is to be converted into vapour at 100°C. The heat required in this process is

• 1028 calorie

• 624 calorie

• 745 calorie

• 810 calorie

The speed of sound in a gas ($\mathrm{\gamma }$=1.5) at 300 K is 340 m/s. The rms velocity of gas molecules will be

• 340  m/s

• $\frac{340}{\sqrt{2}}$ m/s

• 340$\sqrt{2}$ m/s

• 340$\sqrt{15}$ m/s

If 2 g mole of diatomic gas and 1 g mole of monoatomic gas are mixed together, then the ratio of specific heats of mixture is

• 1 : 24

• 1 : 58

• 1 : 46

• 1 : 60