Basic Physics Questions and Answers

In digital communication role of Channel encoder is multiple correct answers To convert analog information signal to digital signal To modulate information signal Add redundant bits to digitally converted information code To convert digital signal signal to analog information You can select

Which is true about aliasing and foldover distortion You can have one or the other but not both Aliasing is a technique to prevent foldover distortion O They are the same thing They are two types of sampling error

a scientist begins with 100mg of a radioactive substance that decays exponentially after 37 hours 50mg of the substance remains How many miligrams will remain after 57 hours

A metallic block with no potential difference applied across it then the mean velocity of free electrons at absolute temperature T is Proportional to T O Proportional to T Zero

12 Which of the following statement s is are incorrect regarding an elastic collision 1 In an elastic collision the linear momentum of system remains constant 2 In an elastic collision the kinetic energy of system remains constant 3 In an elastic collision the final kinetic energy is equal to initial kinetic energy of the system 4 In an elastic collision the final linear momentum is equal to initial linear momentum of the system 13 If both the blocks moving with constant acceleration

3 A bus moves in the curved path as shown 240 km hour 9 km minute x km 2 15 km hour 0 5 5 1Q Which is its average velocity between the P and Q points of travel O 15 km minute 11 t minute

3 2 4 4 In a vernier callipers length of 10 main scale division is 2 mm If 20 vernier scale divisions coincide with 18 main scale divisions then the least count of the instrument is 1 0 1 mm 3 0 01 mm 2 0 2 mm 4 0 02 mm

A rectangular plot of land measuring 0 45 hectors is represented on a map by a similar rectangle of 5 sq cm Calculate RF of the scale Draw a diagonal scale to read single o metre The scale should be long enough to measure up to 400 metres Show a distance of 235 metre on it

An object is thrown in vertically upward direction The time to reach maximum height is 9 VC vo vo 9 vo g V 0 T u 6 V 0 a g Ist u a t 3

An object 5 cm long and a pencil 10 cm long are placed in front of a pin hole camera such that their images have the same length The ratio of the distances of object from the pin hole to that of the pencil is 1 3 2 2 1 2 3 5 2 4 1 4 000

M 21 If a particle of mass m is thrown with speed v at an angle 60 with horizontal then angular momentum of particle at highest point about point of projection 3 mv 16 g mv 3 16 g 2 m 4 3 mv 16 g 3 mv 8 g

39 A body is allowed to fall from altitude 100 m If the time taken in first 50 m is t and for remaining 50 m is t then neglecting air friction 1 t 3 t 2 4 4 Depends on mass

A block of mass m 1 2 kg is attached to a string that is wrapped around the circumference of a wheel of radius R 8 2 cm The wheel rotates freely about its axis and the string wraps around its circumference without slipping Initially the wheel rotates with an angular speed w causing the block to rise with a linear speed v 0 27 m s Figure 1 gure y h V 6 0 1 of 1 111 V 0 Part A Find the moment of inertia of the wheel if the block rises to a height of h 6 7 cm before momentarily coming rest Express your answer using two significant figures VAZO I 0 090 Submit Previous Answers Request Answer Provide Feedback X Incorrect Try Again 4 attempts remaining kg m Ne

3 If four forces act at a point O as shown i the figure and if O is in equilibrium then th value of P are 1 150 10 2N 2 45 10 N 1 3 75 10 2 N 20 N 10N 10 N

A uniformly charged rod is kept on y axis with centre at origin as shown Which of the following actions will increase the electric field strength at the position of the dot dot x Charged rod make the rod longer without changing the charge make the rod shorter without changing the charge make the rod shorter without changing the linear charge density

A satellite is put in an orbit just above the earth s surface with a velocity 1 5 time the velocity for a circular orbit The maximum distance of the satellite from the surface of the earth is nR where R is radius of earth Find n

2 3 5 A proton moves along horizontal line and towards observer the pattern of concentric circular field lines of magnetic field which produced due to its motion 1 ACW In horizontal plane 3 CW In horizontal plane An electron moves along vertical line and towards observer the pattern of concentric circular field lines of magnetic field which is produced due to its motion 1 ACW In horizontal plane 3 CW In horizontal plane A current is flowing in electricity line towards north the direction of magnetic field at a point which is just below the line 1 1 towards north 2 towards south 3 towards east 4 towards west A current is flowing in a vertical wire in downward direction the direction of magnetic field of a point which is just right side to the wire 1 towards north 2 towards south An equilateral triangle of side a carries a current T Magnetic field at point P which is vertex of triangle Hol 2 3ra 2 2 ACW In vertical plane 4 CW In vertical plane Hol 2 3na 2 ACW In vertical plane 4 CW In vertical plane 3 towards east 4 towards west

25 Acceleration a of a particle moving in straight line a a function of velocity v is given as a g kv when g and k are constants If the object starts from res then velocity of the object after very long time is 1 alx 4 2g k ala

5 A small object is moving on a special slope consisting of a concave and a convex circular are both of which have a right angle at the centre and radius R 0 5 m and they join smoothly with horizontal common tangent as it is shown in the figure Determine the distance covered by the object on the slope provided that it started from rest and it detaches from the slope at 3 the altitude R The friction is negligibly small LOT

34 A body A starts from rest with acceleration a After 2 seconds another body B starts from rest with acceleration a If they travel equal distance in 5th second from the start of A then a a equal to 1 5 9 3 9 5 2 5 7 4 9 7

15 The mass of two bodies m and m is given m 2 39 g and m 12 1 g Taking in consideration the significant figures here m m given as 1 14 4 g 2 14 5 g

D The position time graph of a body is given X A B t For the motion between B and C a Velocity increases and acceleration ve velocity decreases and acceleration ve c velocity increases and acceleration is b ve d velocity decreases and acceleration is Fig 3 9 ve

decrease d are true d are true length f produces of the object then mirror is 4 15 cm A square wire of side 3 0 cm is placed 25 cm in front of a concave mirror of focal length 10 cm with its centre on the axis of the mirror and its plane normal to the axis The area enclosed by the image of the wire is 1 7 5cm 3 4 0cm 2 6 0cm 4 3 0cm

A professor was fishing in Durban during the summer holidays of the year 2020 and happened to hook a bag of treasure that sank in the ocean many years ago He pulled the treasure up through the water at a constant speed with a tension of 140 N Calculate the tension he used to lift the bag when it was in the air The densities of the treasure and seawater are 19300 kg m and 1030 kg m respectively

A 10kg watermelon is shot horizontally out of a cannon at 10 m s The melon is shot from a roof 20 meters high 1 How long does it take for the melon to hit the ground use g 10 m s 2 2 How far does it travel in the x direction before hitting the ground

in a new system of unit the unit of mass is unit of length is 100 m and unit of time is Convert one joule into this new system 1 10 unit 2 100 unit 3 7 10 unit 4 1000 unit

Three conducting large plates each of area A are arranged parallel to each other a equal separation d as shown Plates 1 2 and 3 are given charges Q 7Q Q 30 and Q3 2Q respectively Thereafter space between plates 1 and 2 is filled with dielectric of K 2 and plates 1 and 3 are joined by conducting wire The electrostati energy stored in dielectric is B K Q d EA 2Q d A 3

A stone is projected from a point on the ground in such a way so as to hit a bird at height 3h and could attain a maximum height 4h above the ground If at the instant of projection the bird flies away horizontally with speed 10 m s and the stone still hits the bird while descending then the horizontal velocity of stone is A B C D an an 13h 4h 8 ms 1 15 m s 1 12 m s 1 9 m s 1

A certain charge Q is divided at first into two parts q and Q q Later on the charges are placed at a certain distance If the force of interaction between the two charges is maximum then Q q 4 1 Q q 2 1 Q q 3 1

Choose the correct answer 1 A solid sphere of radius R is uniformly charged with charge density p in its volume A spherical cavity of R radius is made in the sphere as shown Then 2 electric potential at the centre of sphere will be 3pR 1 880 O R 2 PHYSIC 5pR 680 3 4

Marks 4 1 mass of M kg is suspended by a weightless string The horizontal force that is required to displace it until the string makes an angle of 45 with the initial vertical direction is Mg 2 1 Mg 2 Mg

Here M m m m and Em r is called the first moment of the mass Further r x i y j z k and TCM XCM YCM 1 ZCM k So the cartesian coordinates of the CM will be or XCM XCM Similarly y CM m x m x mn xn mn m m 11 m x i 1 TCM i 1 M n mi Yi and ZCM m m m3 Substituting the values we get mi zi i 1 M M Example 8 4 The position vectors of three particles of mass m 1 kg m 2 kg and m3 3 kg are r 1 43 k m 1 k m and r3 21 1 2 k m respectively Find the position vector of their centre of mass 5 Sol The position vector of CM of the three particles will be given by m m M3 E3 TCM 91 33 3k 6 n mixi i 1 mi 1 4 k 2 i 3 k 3 21 3 2k 1 2 3 QB x 32 TCM 31 1 k m Example 8 5 Four particles of mass 1 kg 2 kg 3 kg and 4 kg are placed at the four vertices A B C and D of a square of side 1 m Find the position of centre of mass of the particles Sol Assuming D as the origin DC as X axis and DA as Y axis we have Y x y AO

A particle of mass m is driven by a machine that delivers a constant power k watts If the particle starts from rest the force on the particle at time t is A B Correct Answer mdv dt t2 mk t 2 1 2mk t2 1 mkt EXPLANATION Fv constant k V k fvdvfdt

On heating water bubbles being formed at the bottom of the vessel detatch and rise Take the bubbles to be spheres of radius R and making a circular contact of radius r with the bottom of the vessel If r R and the surface tension of water is T value of r just before bubbles detatch is Density of water is p 4441 444444 hl 444 R 2r 44444 14444

Two long straight conductors with current and 12 are placed along x and yaxes as shown in figure The equation of locus of point of zero induction is y O y x Oy 12 x Oy 1 2 x Oy 1 1 x 12 X

In a double mass system two masses one of mass m and the other of 2m d distance apart rotate about their common centre of mass Find the value of the period of revolution in sec 10 10 Nm kg m 2 1020 kg G d 2 3 4 104 m

Convex lens made up of glass g 1 5 and radius of curvature R is dipped into the water Its focal length will be Refractive index of water 4 3 A 4R B 2R CR D R2

None these Power of a convex lens is 5D 1 5 this lens is immersed in a liquid of refractive inde it acts like a divergent lens of focal length 10 cm Then refractive index of the liquid will be 2 e 5 3 3 6 5 teleghyn 4 None of these

A horizontal uniform glass tube of 100 cm length sealed at both ends contains 10 cm mercury column in the middle The temperature and pressure of air o either side of mercury column are respectively 31 C and 76 cm of mercury If the air column at one end is kept at 0 C and the other end at 273 C the pressure of air which is at 0 C is in cm of Hg Assume no heat flow through mercury A B C 76 Your Answer 88 2 102 4 Correct Answer 12 2 EXPLANATION o o

Two blocks B and C are connected with a spring of stiffness k A block A is projected with speed v as shown For what value s of I will the block D move with velocity v after all the elastic collisions are over All the blocks have mass m and surface is smooth A D A m TV E m 2k E B k 00000 C D V

Two wires A and B made of same material and having their lengths in the ratio 6 1 are connected in series The potential difference across the wires are 3V and 2V respectively If r and are the radii of A and B respectively then IB rA 1 2 1 2 3 1 is 4 2

A charged particle having some mass is resting in equilibrium at a height H above the centre of a uniformly charged non conductin horizontal ring of radius R The force of gravity acts downwards The equilibrium of the particle will be stable

A body runs on a circular path of radius R 28m with a constant speed u 4 m s Another boy starts from the center of the path to catch the first boy The second boy always remains on the radius connecting the center of the circle and the first boy and maintains the magnitude of his velocity V 4 m s If the time of chase is x sec then mark x YOUR ANSWER 44

A square shaped coil of N turns and side a is rotating with angular velocity w about an axis passing through its centre and perpendicular to its plane A uniform magnetic field of magnitude B exists parallel to the axis of rotation The maximum emf developed in the coil will be O Na Bw O O Na Bo 2 Na Bo 4 O Zero

Which of the following situations is possible a An object can have acceleration but constant velocity b The velocity of an object may be zero but acceleration is not zero c Distance and the magnitude of displacement are equal in circular motion d Average speed and the magnitude of average velocity are always equal in circular motion

A loudspeakersystem uses alternating current to amplify sound of certain frequencies It consists of two speakers in parallel Tweeter which has a smaller diameter produces high frequency sound Woofer which has larger diameter produces low frequency sound For purpose of circuit analysis we can take both speakers to be of equal resistance R The equivalent circuit is shown in the figure Select the correct alternative B R www R www mmmmm e e sin oot o The speaker connected with the capacitor acts as woofer The speaker connected with the Inductor acts YOU MARKED X

A wooden block of mass m resting on a rough horizontal table coefficient of friction u is pulled by a force F as shown in figure The acceleration of the block moving horizontally is Fcose sing M

The antenna current of an AM transmitter is 8 A when only the carrier is sent but it increases to 8 93 A when the carrier is modulated by a single sine wave Find the percentage modulation A B 60 1 D 70 1 C 80 1 50 1

Three rods of the same length and the same area of the cross section are joined The temperature of two ends one T and T as shown in the figure T K T Temperature As we move along the rod the variation of temperature are as shown in the following Rods are insulated from the surrounding except at the faces B T 30 K2 04 4 4 K 3 3 L Length 45 K3 1 K K2 K3 4 4 8 0 1 K K K 3 4 K3 3 1 K 2L 60 K 3L T

What is the strength of transverse magnetic field required to bend all the photoelectrons within a circle of a radius 50 cm when light of wavelength 3800 A is incident on a barium emitter Given that work function 34 of barium is 2 5 eV h 6 63 10 J s e 1 6 10 19 C m 9 1 x 10 kg 31 A D 4 88 10 4 T 32 10 5 T 6 32 x 10 6 T 7 6 10 8 T