11.

n balls each of mass m impinge elastically each second on a surface with velocity v. The average force experienced by the surface will be

• 2nmv

• nmv

• $\frac{\mathrm{nmv}}{2}$

• 4nmv

A monkey of mass 30 kg climbs on a massless rope whose breaking strength is 450 N. The rope will break if the monkey (Take g = 10 m/s² )

• climbs up with a uniform speed of 5 m/s

• climbs down with an acceleration 4 m/s²

• climbs up with an acceleration 6 m/s²

• climbs down with a uniform speed of 5 m/s²

The angle to which a cyclist bends when he covers a circular path of 34.3 m in $\sqrt{22}$ s is

• 20°

• 30°

• 60°

• 45°

A gun of mass M fires a bullet of mass m with velocity v. Then, the recoil speed of the gun will be

• $-\frac{\mathrm{m}}{\mathrm{M}}\mathrm{v}$

• $\frac{2\mathrm{m}}{\mathrm{M}}\mathrm{v}$

• $\frac{\mathrm{M}}{\mathrm{m}}\mathrm{v}$

• $\frac{2\mathrm{M}}{\mathrm{m}}\mathrm{v}$

A solid sphere of radius r made of a material of bulk modulus K is surrounded by a liquid in cyliridrical container. The massless piston of area A floats on the surface of the liquid. If a mass m is placed on a piston to compress the liquid, then the fractional change in the radius of the sphere will be

• $\frac{\mathrm{mg}}{\mathrm{AK}}$

• $\frac{2\mathrm{mg}}{\mathrm{AK}}$

• $\frac{3\mathrm{mg}}{\mathrm{AK}}$

• $\frac{\mathrm{mg}}{3\mathrm{AK}}$

If a liquid is flowing through a horizontal tube, then $\mathrm{p} + \frac{1}{2}{\mathrm{\rho V}}^2$= constant. This shows that

• If p increases then V also increases

• p and V both are constant

• If p increases then V decreases

• If p decreases then V also decreases

Water wets the walls of its glass container due to the fact that

• cohesive force is greater than adhesive force

• cohesive force is equal to the adhesive force

• adhesive force is greater than the cohesive force

• cohesive and adhesive forces form action-reaction pair

A lift is ascending with an acceleration $\frac{\mathrm{g}}{3}$ . A simple pendulum suspended from its ceiling oscillates with a period T. The period of oscillation of pendulum when the lift is stationary will be

• $\frac{1}{\sqrt{3}} \mathrm{T}$

• T

• 2 T

• $\frac{2}{\sqrt{3}} \mathrm{T}$

A stationary source emits a sound moving towards a wall with a velocity u. Speed of sound in air is v. The fractional change in the wavelength of the sound sent and the reflected sound is

• $\frac{\mathrm{v} + \mathrm{u}}{\mathrm{v} - \mathrm{u}}$

• $\frac{2\mathrm{u}}{\mathrm{v} + \mathrm{u}}$

• $\frac{2\mathrm{v}}{\mathrm{v} + \mathrm{u}}$

• $\frac{\mathrm{u} + \mathrm{v}}{2\mathrm{v}}$

Mass of 1 mol of air is 29 x 10^-3 kg. The speed of sound at STP will be nearly

• 332.5 m/s

• 340 m/s

• 320 m/s

• 325 m/s