Basic Physics Questions and Answers

8 A thick walled hollow sphere has outer radius R It rolls down an inclined plane without slipping and its speed at the bottom is v If the inclined plane is frictionless and the sphere slides down without rolling its speed at the bottom is 5v 4 What is the radius of gyration of the sphere R 1 3R 3 2 4 R 2 3R

In which of the following cases forces may not be required to keep the 1 Particle going in a circle 2 Particle going along a straight line 3 The momentum of the particle constant 4 Acceleration of the particle constant

42 In the equation for a stationary wave given by TUX y 5 cos sin 100 t Here x is in cm and t in 25 second A node will not occur at distance x a 25 cm c 12 5 cm b 62 5 cm d 37 5 cm

55 The spectral emissive power against wavelength graph of a black body emitting radiations are shown in the figure at two different temperatures T 27 C and T 327 C If the total power emitted at temperature T is P What is the area of the shaded portion e 40 1 15 P 3 16 P T 60v T 300k 2 2 8 P 4 7 PST 3 10

2 6 The moment of inertia of a body rotating about a given axis is 12 0 kg m in the SI system What is the value of the moment of inertia in a system of units in which the unit of length is 5 cm and the unit of mass is 10 g a 2 4 10 X c 5 4 x 105 b 6 0 10 d 4 8 x 105

3 22 m s 4 80 m s 17 The displacement time graph of two moving objects A and B are shown in the figure given below Which of the following is incorrect 1 B is moving with constant velocity 2 A is moving with increasing speed 3 B is moving with non zero constant acceleration Acceleration of A may be constant B for its speed is reduced to half of its initial valu

3 LV3 4 None of these Work done in time t on a body of mass m which 6 is accelerated from rest to a speed v in time t as a function of time t is given by 1 2 m 1 3 my 4 3 v3 8 1 3 falan fan mv 4 4 eld

In the circuit shown the current through the 4 Q resistor is 1 A when the points P and M are connected to a d c voltage source The potential difference between the points M and N is Po A B C 0 522 0 5 volts 422 0 592 3 2 volts 352 1 5 volts N www 12 M Correct Answer My Answer

An oil drop of radius r and density p is held stationary in a uniform vertically upwards electric field E If Po p is the density of air and e is quanta of charge then the drop has 4xr P Po g excess electrons 3eE 4xr p Po g excess electrons CE deficiency of 4 P P electrons 3eE 105 attempts EXPLANATION 15 24 got it right nel p po g i e n 3 For equilibrium electric force must be upwards i e charge on the drop is positive 4 r P Po g 3eE 1m 39s avg time A r p pal electrons Medium Correct

A ball of mass 0 5 kg moving with a velocity of 2 m sec strikes a wall normally and bounces back with the same speed If the time of contact between the ball and the wall is one millisecond the average force exerted by the wall on the ball is 1 2000 N 2 1000 N 3 5000 N

A man is standing at a spring platform Reading of spring balance is 60 kg wt If man jumps outside platform then reading of spring balance 1 First increases then decreases to zero 2 Decreases 3 Increases

4 A bubble of air is underwater at temperature 15 C and the pressure 1 5 bar If the bubble rises to the surface where the temperature is 25 C and the pressure is 1 0 bar what will happen to the volume of the bubble a Volume will become greater by a factor of 1 6 b Volume will become greater by a factor of 1 1 c Volume will become smaller by a factor of 0 70 d Volume will become greater by a factor of 2 5

17 A new unit of length is chosen such that the speed of light in the vacuum is unity What is the distance between the Sun and the Earth in terms of the new unit if light takes 8 min and 20 sec to cover this distance 1 500 new units of length 2 100 new units of length 3 300 new units of length 4 200 new units of length The figur dimensio time are interval X

A sample of ideal gas Degree of freedom f 5 is heated at constant pressure If an amount 140 J of heat is suplied to the gas the work done by the gas is 1 25 J 2 40 J 3 35 J 4 201

Find the time period of revolution of a planet around the sun which is at a distance of 5 A U from the Sun Distance of the Earth from the Sun is 1 A U Options 1 5 365 5 days 2 V 365 5 days 3 360 days 4 None of these

Earth is flattened at the poles and bulges at the equator This is due to the fact that a the Earth revolves around the sun in an elliptical orbit b the angular velocity of spinning about its axis is more at the equator c the centrifugal force is more at the equator than at poles d none of these

In the arrangement shown in figure sin 37 3 5 0 7 10 kg 4 kg the 39 fer ff sin 37 37 1 Direction of force of friction is up the plane 2 The magnitude of force of friction is zero 3 The tension in the string is 20 N 4 Magnitude of force of friction is 56 N H 0 7 370 10 kg 1 for fem 2 3 20 N 4 56 3 5 4 kg

3 3 1 4 3 1 The variation of velocity of a particle moving along a straight line is as shown in the figure given below The distance travelled by the particle in 5 s is 1 60 m 3 40 m m s V 20 10 t 0 A B DE C 4 5 t s 1 2 3 2 30 m 4 50 m 24 Pusa Road New Delhi 110005 Ph 011 47

At a place the horizontal component of Earth s magnetic fields is 50 microtesla A bar magnet of magnetic moment 4 Am is free to rotate about a vertical axis passing through its centre The magnet at rest is released from East West position The kinetic energy acquired by the magnet when it aligns to North South position is O 50 J O 100 J O 200 J O 400 J

If it rains a dealer in umbrella can earn Rs 260 per day and if it does not rain he loses Rs 70 per day Then his expectation if the probability of a rainy day is 0 56 is YOU A 112 8 B 114 8

A rocket with a lift off mass 2 104 kg is blasted upwards with an intial acceleration of 5 m s 2 The initial thrust of the blast is Take g 10 m s 1 2 x 105 N 3 4 105 N 2 3 105 N 4 5 105 N

1 Three identical thin rods each of length L and mass m are welded perpendicular to one another as shown in figure The assembly is rotated about an axis that passes through the end of one rod and is parallel to another The moment of inertia of this structure about this axis is 7 1 ml 12 3 2 ml 12 2 N Axis of rotation 1m1 14 4 ml y X

0 A bullet of mass m and charge q is fired towards a solid uniformly charged sphere of radius R and having total charge q If it strikes the surface with speed u then find the minimum speed u so that it can penetrate through the sphere neglect all resistance forces acting on bullet except electrostatic force 1 q m q 2TE MR 7 2 q 4 E MR

5 The pressure exerted by 6 0 g of methane gas in a 0 03 m vessel at 129 C is Atomic masses C 12 01 H 1 01 and R 8 314 J K mol a 215216 Pa b 13409 Pa c 41648 Pa d 31684 Pa Mains 2010

are two infinite slabs of charge both of thickness d with the junction lying on the plane x 0 The slab lying in the range 0 x d has a uniform charge density p and the slab lying in the region d x 0 has uniform charge density p Find the Electric field everywhere and plot its variation along the x axis Note This can be used to model the variation of electric field in the depletion layer of a p n junction

The curved surface of a very long hollow non conducting cylinder of radius R is uniformally charged with surface charge density o A non conducting small circular ring of radius a and mass m having charge q uniformly distributed over its length is placed coaxially inside the hollow cylinder at its centre The arrangement is located in a gravity free space o R o If the cylinder is rotated with a constant angular velocity o about its axis as shown in the figure Then the angular velocity acquired by the ring is

A bar magnet of magnetic moment M is bent to form an arc as shown in figure The magnetic moment of new magnet is O O O O 190 2 2 3x 2M M M 24 M

In a vibration magnetometer the time period of oscillation of a bar magnet is 2 s The magnet is cut transversely in two equal parts and tied over sach other so that like poles are together The new time period of vibration will be O O 1s 2 s O 4s

A perfectly reflecting mirror of mass m and exposed surface area A is exposed to electromagnetic radiation of intensity I on a rough horizontal surface 1 with friction co efficient u 3 mgc IA The minimum value of pulling force required to exert on mirror to move the mirror is 1 4 m 3 as shown 2 where c is speed of light is 2 mg 2 4 4 F 3 The value of

3 A function is y x The approximate value of 43 the function at x 2 0001 is possibly choose the closest answer possible 1 8 0006 3 8 0012 2 8 0008 4 8 0015 H hely x 1x2 0001 1 8 0006 0 0010 F 2 8 0008 0 001

3 0 r A particle starts from the origin goes along x axis to the point 10 m 0 and then returns along the same line to the point 10 m 0 The distance and displacement of the particle during the trip are 4 Tr O 1 20 m 0 2 30 m 10 m 2 30 m 10 m 420 m 10 m ling and comes back to ito in quantity

The magnetic force acting on a charged particle of charge 4 C moving with velocity 1 2 x10 m s in a magnetic field of 3 T acting in x direction is O9 N in z direction 24 N in z direction O9 N in y direction O24 N in y direction

3 b and c 4 a b and c 5 Two masses of 20 kg and 30 kg respectively are 45 connected by a massless spring as shown in the figure A force of 200 N acts on the 30 kg mass At the instant shown the 20 kg mass has an acceleration 2 m s rightwards What is the acceleration of 30 kg mass 20 kg 1 Zero 2 5 3 m s 3 4 m s 4 8 m s 0000000000000 30 kg 200N 3 bac 20 kg 30 kg a eu 2 200 NT 30 kg at 30 kg are t 20 kg 4 a bac 1 Zero 2 5 3 m s 20 kg ar 2 m s 3 4 m s 4 8 m s fanger fein voorsor i 2 faxeft 30 kg 200N

The magnitude of physical quantity is I The product of numerical value and unit 2 The ratio of numgical value and unit 3 The sum of numerical value and unit 4 The difference between numerical value and unit

a wooden block After 1 h of this instant the boat turns back and crosses the wooden block again at some point of time at a point that is at 6 km from the first crossing Find the velocity of the river MAIN Solution Taking the rightward direction as positive x axis Given The distance between the first crossing and the second crossing is 6 km Let the velocity of the river be v Taking the wooden block as the frame of reference The wooden block flows with the river and therefore the velocity of the wooden block is the same as the velocity of the river i e V 6 km y Since the speed of the boat with respect to the wooden block is constant therefore time taken by boat to move forward and come backwards will be equal i e 1 1 2 hr So the wooden block flows for a total of 2 hours before meeting the boat again Therefore tance travelled by wooden block in 2 h is equal to the distance between the first crossing the second crossing which is 6 km v x 2h 6km v 3kmh

A liquid is kept in a cylindrical vessel which is rotated about its axis The liquid rises at the sides If the radius of the vessel is 0 05 m and the speed of rotation is 2 rev s the difference in height of the liquid at the centre of vessel and its sides is Options

Two concentric coils each of radius equal to 2 cm are placed at right angles to each other 3A and 4A are the currents flowing in each coil respectively in anticlockwise direction The magnetic field in T at the centre of the coil will be Oa 12 X 10 5 Ob 10 5 c 5 X 10 5 d 7 X 10 5 CAAK OO

A clear sheet of polaroid is placed on top of similar sheet so that their axis make an angle sin 1 3 5 with each other The ratio of intensity of final emergent light to that of unpolarised light incident is 16 25

AT WHAT TEMPERATURE THE READING OF FARENHEIT SCALE IS TWICE THAT ON CEL CIUS AND CELCIUS SCALE AND KELVIN SC ALE SIR MAM PLEASE SOLVE THIS QUESTION ON THE PIECE OF PAPER SO SIR MAM IT W ILL BE HELPFUL FOR ME

The values of d and d for final rays to be parallel to the principal axis are Focal lengths of the lenses are written on the lenses 10 cm 0 10 cm d d 10 cm d 15 cm d 20 cm d 15 cm d 30 cm d 15 cm d 40 cm d 15 cm 20 cm 5 cm X d

A luminous point source is placed at a depth of 30 cm in a vessel containing a liquid of refractive index 1 25 From the source light rays are being emitted in all directions The rays which are refracted from the upper surface of the liquid form a circle Calculate the radius of the circle 40 cm

15 cm concave mirror is moving with velocity 47 21 cm s whereas a point object is moving with 87 11 cms as shown in figure The object is at a distance of 15 front of mirror whose focal length is 10 cm The axial velocity of image is v then 1 4xn find the value of n nswer 0 01 02 4 5 06 07 08

An electron and a proton are revolving around common center O in two coplanar circular paths as shown in figure with time period of rotation 1 s and 2 s respectively The net magnetic field at O will be Hoe 1 tesla TT Hoe 2 Z tesla 3 2 e tesla 4 Zero e e 11m 2m

5 A source of light is placed at the bottom of a tank filled with water up to the height of 80 cm Calculate the area at the surface of water through which light rays will be emitted Refractive index of water 1 33 2 6 m

1 A glass is filled with water up to 12 5cm The apparent depth of an object lying at the bottom of the glass is mea sured by a microscope to be 9 4cm Calculate the refrac tive index of water If water is replaced by a liquid of 750 refractive index 1 63 up to the same height by what dis tance would the microscope has to be moved to focus the object again NCERT 1 33 1 74 cm

For a series LCR circuit in resonance 1 If value of R is changed then voltage across inductor V and voltage across capacitor Vc also change 2 If value of R is changed then voltage across inductor V and voltage across capacitor V remains unchanged 3 Voltage drop across L C combination remains unchanged on changing value of R 4 Voltage drop across L C combination changes

3 12 m 4 None of above A very broad lift is going vertically upwards with 27 a constant acceleration of 2ms At the instant when its velocity is 4ms a ball is projected from the floor of the lift with a speed of 4ms relative to the floor at an angle 30 with horizontal The time of flight of the ball in the lift is g 10 ms 2 1 s 2 s 4 Is 3 12 m harga frega fere 2 2 site an effet de 8 at fere et 30 free sarfa fram a 3 4 340 fer g 10ms 4msi at el 4 ms 4 1s

In a circuit L C and Rare connected in series with an alternating voltage source of frequency f The curren leads the voltage by 45 The value of Cis O O 1 2nf 2nfL R 1 nf 2nfL R 1 2nf 2nfL R

The system have initial configuration as given in the figure inextensible m Now The bob is released and the string starts wrapping around the pulley The pulley is held in place by a force applied at the centre Given that string and the pulley are light What is the tension in the string as a function of B AT 3mg sin 0 2mg 1 cos 0 2mgl Ro T 3mg sin 0 T 2mg sin 0 1 cos 8 mgR 1 RO Cos 0

configuration as given in the figure inextensible 22 Now The bob is released and the string starts wrapping around the pulley The pulley is held in place by a force applied at the centre Given that string and the pulley are light 15 What is the tension in the string as a function of 0 T 3mg sin 0 2mg 1 cos 0 T 3mg sin 0 T 2mg sin 0 2mgl Re 1 cos 0 mgR 1 RO cos