Physics

A point object moves towards a concave mirror with a speed $10\mathrm{c}\mathrm{m}{\mathrm{s}}^{-1}$ along the principal axis. The magnitude of the velocity of object with respect to image when the object is at distance of 15cm from the pole is __ $\mathrm{c}\mathrm{m}{\mathrm{s}}^{-1}$ . (Focal length of the mirror kept at rest is 10cm )

Two carnot engines operate in series between a heat source at a temperature $T_1=900\mathrm{K}$ and heat sink at temperature $T_3=400\mathrm{K}$ . There is another reservoir at temperature $T_2$ , as shown, with $T_1>T_2>T_3$ . The two engines are equally efficient if $T_2=$ K 

A paramagnetic sample shows a net magnetisation of $12\mathrm{A}/\mathrm{m}$ when placed in an external magnetic field of $0.6\mathrm{T}$ at a temperature of $4\mathrm{K}$ . When the same sample is placed in an external magnetic field of $0.2\mathrm{T}$ at temperature of 16 k, the net magnetisation will be $\mathrm{A}/\mathrm{m}$ .

A hot body is being cooled in air according to Newton's law of cooling, the rate of fall of temperature being K times the difference of its temperature with respect to that of surroundings. The time after which the rate of heat loss of the body will be half of the maximum rate of heat loss is $\frac{1}{2k}{\mathrm{l}\mathrm{o}\mathrm{g}}_e?n$ (The time is to be counted from the instant t = 0 ). The value of n is

A 1kg particle is moving unidirectionally on a horizontal plane under the action of power $P=-2v^3$ , of power supplying energy source. The velocity (v) - time (t) graph that describes the motion of the particle is shown in figure. (Graphs are drawn schematically and are not to scale) The value of $t_0$  in graph is sec. Find 8x

A circular loop of radius R = 20 cm is placed in a uniform magnetic field B = 7 T in x-y plane as shown in figure. The loop carries a current $i=1.0\mathrm{A}$ in the direction shown in figure. The magnitude of torque acting on the loop is__ N.m. Take $\left.\pi =\frac{22}{7}\right\}$

 

A circular loop of radius R= 20cm is placed in a uniform magnetic field b= 7 T in x-y plane as shown in figure. The loop carries a current $i=1.0\mathrm{A}$ in the direction shown in figure. The magnitude of torque acting on the loop is__ N.m. Take $\left.\pi =\frac{22}{7}\right\}$

Three points masses $m,2m$ and 3m are located at the vertices of an equilateral triangle of side ' a '. The moment of inertia of the system about an axis along the altitude of the triangle passing through m is $\frac{N}{20}m{a}^2$ where N is an integer. The value of N is

Block of mass M slides down on frictionless incline as shown. The minimum friction coefficient so that block of mass m does not slide with respect to lower block is close to $\frac{I}{1000}$ , the nearest integer to I is $?\left(\mathrm{s}\mathrm{i}\mathrm{n}?{37}^{?}\approx \frac{3}{5}\right)\left\{\right.$ Take $\left.g=10\mathrm{m}/{\mathrm{s}}^2\right\}$

A $100\mathrm{e}\mathrm{V}$ electron collides with a stationary helium ion ${\mathrm{H}\mathrm{e}}^{+}$ in its ground state and excites it into higher energy level $n$ . After collision ${\mathrm{H}\mathrm{e}}^{+}$ ions emits two photons in succession with a wavelength $1085\text{?}$ and $304\text{?}$  to reach its ground state. Quantum number of excited state $n$  is