# Recent questions and answers in Class11

### A total of $\$10000$is distributed among$150$person as gift. A gift is either of$ \$50$ or $\$100$. Find the number of gifts of each type. ### A 150 m long train is moving with uniform velocity of 45 km/h. The time taken by train to cross the bridge of length 850 m is ? ### The torque$\overrightarrow{z}$on a body about a given point is found to be$ \overrightarrow{A} \times \overrightarrow{L}$where$\overrightarrow {A}$is a constant vector and$\overrightarrow{L}$is angular momentum about that point . From this it follows that. 1)$\large\frac{dL}{dt}$is perpendicular to$\overrightarrow {L}$at all times 2) the component of$\overrightarrow {L}$in the direction of$\overrightarrow{A}$does not change with time. 3) the magnitude of$\overrightarrow {L}$does not change with time. 4)$\overrightarrow {L}$does not change with time. Which of the following is correct? ### A wire of length L and cross-sectional area A is made of material of Young's modulus Y. The work done in stretching the wire by an amount x is given by ### Three closed vessels A , B and C are at the same temperature T and contain gases which obey maxwellian distibution of velocities . Vessel A contains only$\;O_{2}\;$. B only$\;N_{2}\;$and C a mixture of equal quantities of$\;O_{2}\;$and$\;N_{2}\;$. If the average speed of$\;O_{2}\;$molecules in vessel A is$\;V_{1}\;$, that of$\;N_{2}\;$molecules in vessel B is$\;V_{2}\;$the average speed of the$\;O_{2}\;$molecules in vessel C will be ### Two blocks are in contact on a frictionless table. One has mass m and another mass '2m'. A force F is applied on '2m' as shown. Now the force F is applied on 'm' from right. In the two cases respectively the ratio of force of contact between the blocks is ### A uniform circular disc of radius r is placed on a rough horizontal surface and given a linear$w_0$as shown. The disc com,es to rest after moving some distance to the right. It follows that ### A block takes twice as much time to slide down a rough$45^{\large\circ}$inclined plane as it takes to slide down an identical smooth$45^{\large\circ}$inclined plane.The coefficient of kinetic friction between the block and the rough inclined plane is ### Hot air balloon is an application of what law? ### The motion of a sphere moving on a rough horizontal surface change from pure sliding (without rolling) to pure rolling (with out slipping) . In this process, the force of friction. 1) initially acts opposite to the direction of motion and later in the direction of motion. 2) causes linear retardation 3) causes angular acceleration 4) stops acting when pure rolling begins. Which of the following is correct? ### A solid sphere of mass m is lying at rest on a rough horizontal surface. The coefficient of friction between the ground and sphere is$\mu$. The maximum value of F, so that the sphere will not slip is equal to ### A body covers a certain distance x in equal thirds - the first third of distance with speed v$_1$, the second third with a speed of v$_2$and the last third with a speed of v$_3$. What is the average speed of the body over time? ### A spherical body of radius R rolls on a horizontal surface with linear velocity$V$. Let$L_1$and$L_2$be the magnitude of angular momentum of the body about the centre of mass and point of contact P respectively. a)$L_2=L_1$if radius of gyration$k=R$b)$L_2=2L_1$for all cases. c)$L_2 > 2L_1$if radius of gyration$K < R$d)$L_1> L_2$if radius of gyration$ K > R$Which of the following is correct? ### Which of the following does not represent Boyle's law? ### A ball is dropped from a height of h from ground. If the coefficient of restitution is e, the height to which the ball goes up after it rebounds for the nth time is ### A man spinning in free space changes of his body e.g by spreading his arms and curling up. By doing this, he can change his 1) moment of inertia 2) angular momentum 3) angular velocity 4) rotational kinetic energy in this Which of the following is correct? ### A horizontal disc rotates freely about a vertical axis through its centre. A ring, having the same mass and radius as the disc , is now gently placed on the disc. After some time, the two rotate with a common angular velocity. 1) some friction exits between the disc and the ring 2) the angular mometum of disc plus ring is conserved. 3) the final common angular velocity is$\large\frac{2}{3}$rd of the initial angular velocity of disc. 4)$\large\frac{2}{3}$rd of the initial kinetic energy is converted to heat. Which of the following is correct? ### From the top of a building 40 m tall, a ball a thrown vertically upwards with a velocity of$10\; ms^{-1}$After how long will the ball hit the ground? ### A person sitting in an open car moving at constant velocity throws a ball vertically up into air. The ball falls ### Find the dimension of physical quantity$X$in the equation$Force=\large\frac{X}{Density}$### In the circuit as shown in the figure what is the potential difference between P and Q. ### The trajectory of a projectile in a vertical plane is$y=ax-bx^2$where$a$and$b$are constants. The maximum height attained by the particle and the angle of projection from horizontal are ### a body is projected vertically upward from the earths surface such that it reaches a height equal to the radius of the earth above its surface.find the velocity of projection ### A 150m long train is moving with uniform velocity of 45km / h. The time taken by train to cross the bridge of length 850m is ? ### Dhoni throws his bat vertically upwards with an initial velocity of$26.2\;m/s$Determine the height to which the bat will rise above its initial height. ### Two identical ladders are arranged as shown in the figure, resting on a horizontal surface. Mass of each ladder is M and length L. A block of mass m hangs from the apex point P. If the system is in equilibrium, find direction and magnitude of friction force acting at A or B. ### A particle of mass m is travelling with a constant velocity$\overrightarrow {V} =V_0 \hat i$along the line$y=b,z=0$. Let$dA$be the area swept out by the position vector from the origin to the particle in time at end L be the magnitude of angular momentum of particle about orgin at any time t. Then 1) L= constant 2)$\large\frac{dA}{dt}=\frac{L}{m}$3)$\large\frac{dA}{dt}= \frac{2L}{m}$4)$\large\frac{dA}{dt}=\frac{L}{2m}$Which of the following is correct? ### Six equal resistance are connected between point P,Q,R as shown in the fig. Then the net resistance will be maximum between ### A solenoid carrying a current supplied by a DC source with constant emf contains iron rod inside it. when the rod is pulled out of the solenoid , then the current in the solenoid will ### In an AC circuit V and I are given by$V=100 \sin (100 t) volt \; I =100 \sin (100 t +\large\frac{\pi}{3})amp$the power dissipated in the circuit is ### An aeroplane is moving north horizontally , with a speed of$200 ms^{-1}$,at a place where the vertical component of the earth's magnetic field is$ 0.5 \times 10^{-4}\;T$.What is the induced e.m.f set up between the tips of the wings, if they are 10 m apart ? ### If vectors$\overrightarrow{A} = \cos wt \hat i +\sin w + \hat j$and$\overrightarrow{B} = \cos wt/2 \hat i +\sin wt/2 + \hat j$are functions of time , then the value of t at which are orthogonal to each other is ### A child is standing with his two arms outstretched at the center of a turntable that is rotating about its central axis with an angular speed$w_0$Now the child folds his hands back so that the moment of inertia becomes 3 times the intial values.The new angular speed is ### Three planets of same density and with radii$R_1,R_2$and$R_3$Such that$R_1=2R_2=3R_3$, have gravitational fields on the surfaces$E_1,E_2,E_3$and escape velocities$v_1,v_2,v_3$respectively ,then ### A block of wood floats in water with$\large\frac{4}{5}$th of its volume submerged , but it just floats in a liquid . What is the density of the liquid ? ### A clock with an iron pendulum beeps correct time at$15 ^{\circ}c$what will be the error in time per day , if the room temperature is$20^{\circ}$? ### A charge q is placed at the centroid of an equilateral triangle. Three charges equal to Q are placed at the vertices of the triangle . The system of the four charges will be in equilibrium . if q is equal to ### Two H atoms in the ground state collide elastically. The maximum amount by which their combined kinetic energy reduced is ### The total energy in the ground state of hydrogen atom is$ -13.6\;eV$. The kinetic energy of this electron in first excited state is : ### Ina common emitter configuration, a transistor have$\beta= 50$and input resistance$1k \omega$. If the peak value of a.c input is$0.01\;V$then the peak value of collector current is ### A ratio station has two channels . one is AM at$1020 kHz$and the other FM at$89.5$MHz. For good results you will use ### A ball is dropped to the ground from a height of 8 m. The coefficient of restitution is 0.5 . To what height will the ball rebound? ### An astronaut is looking down on Earth's surface from a space shuttle at an attitude of 400 km. Assuming that the assonants pupil diameter is 5 mm and wave length of visible light is 500 nm, the assonant will be able to resolve linear objects of the size of about ### The second overtone of an openpipe has the same frequency as the first overtone of a closed pipe 2m long . Calculate the length of the open pipe . ### A horizontal platform with an object placed on it is executing is$3.92 \times 10^{-3}\$ what must least period of these oscillation , So that the object is not detached from the platform?

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