1971 + Interview Questions in Physics in Class 9 Page 39 InterviewSolution

1901.	A porter lifts a luggage of 15 kg from the ground and puts it on his head 1.5 m above the ground. Calculate the work done by him on the luggage.
Answer» Solution :MASS of luggage `m=15kg`, DISPLACEMENT `s=1.5m` Work done `W=Fxxs` `=mgxxs` `=15kgxx10ms^(-2)xx1.5m` `=225(kgms^(-2))m` `=225Nm=225J` Work done is 225 J.

Discussion

1902.	Express the relationship between the C.G.S. and S.I. units of density.
Answer» ANSWER :`1GM^(-3)=1000kgm^(-3)`

Discussion

1903.	What are the two factors that influence buoyancy.
Answer» ANSWER :DENSITY of the LIQUID and VOLUME of the OBJECT.

Discussion

1904.	A glass slab ABCD is made of two different grades of glass of refractive indices 3/2 and 4/3 of equal thickness, and a ray PQis incident on theface AB. Trace theray as it passes through theslab and find theangle of emergence and the angle of deviation, Find theeffective refractive index of the slab.
Answer» Solution :(i) Apparent shift ` = t(1-1/mu)` Find theapparent shift in each glass slab `S_(1) and S_(2)` and the total shift (S) = `S_(1) + S_(2)` But `S = t(1-1/mu_(e))` when `mu_(e)` is the EFFECTIVE refractive INDEX (ii) `mu = 24/17`

Discussion

1905.	Complete the following: 1 m = .............. Å
Answer» SOLUTION :`10^(10)`

Discussion

1906.	Four men lift a 250 kg box to a height of 1 m and hold it without raising or lowering it. (i) How much work is done by men in lifting the box? (ii) How much work is done in just holding it? (Take g=10ms^(-2)).
Answer» Solution :Here, `m=250kg, h=1m, g=10ms^(-2)`. Weight of the box = force = `mg=250xx10N` `=2500N` Work DONE = mgh = `2500Nxx1m` `=2500Nm` `=2500J` (ii) When the box is just hold, there is no DISPLACEMENT. `therefore` The work done is zero, even though the men GET TIRED.

Discussion

1907.	In Physics, energy is an indirectly observed quantitythat is often understood as the ability of a physical system to do work on other physical system. However, this must be understood as an ovberly simplified definition as we shall come to know in higher classes that not all energy can perform work. (a) How did the concept of energy emerge ? (b) How much electric energy is generated in a typical lightning strike ? What are the forms to which this energy gets converted ? (c ) What is the kinetic energy of a passenger seated in a moving plane : (i) with respect to theplance (ii) wiht respect to the Earth.
Answer» SOLUTION :The concept of energy emerged out of the IDEA of Vis Viva (living force) and it was believed that total Vis Viva was conserved. (b ) 500 mega Joules. Light energy, sound energy, thermal energy, etc. (c ) (i) Zero (II) Non - zero KINETIC energy (and higher total energy).

Discussion

1908.	A body floats in a liquid A of density rho_(1) with a part of it submerged inside liquid while in liquid B of density rho_(2) totally submerged inside liquid. The densities rho_(1) and rho_(2) are related as :
Answer» `rho_(1)=rho_(2)` `rho_(1)ltrho_(2)` `rho_(1)gtrho_(2)` NOTHING can be said Answer :C

Discussion

1909.	On increasing the resistance in a circuit, the current in it:
Answer» decreases increases remains unchanged nothing can be said Answer :A

Discussion

1910.	We come across various activities which we normally consider to be work in day-to-day life. for each of these activities, ask the following questions and answer them : Who (What) is doing work?
Answer» SOLUTION :The ONE EXERTING the FORCE is doing WORK.

Discussion

1911.	We come across various activities which we normally consider to be work in day-to-day life. for each of these activities, ask the following questions and answer them : What is happening to the object?
Answer» SOLUTION :The OBJECT MOVES DUE to the applied force.

Discussion

1912.	We come across various activities which we normally consider to be work in day-to-day life. for each of these activities, ask the following questions and answer them : What is the work being done on?
Answer» SOLUTION :A FORCE is being APPLIED on an OBJECT.

Discussion

1913.	A body, initially at rest, starts moving with a constant acceleration 2 ms^(-2). Calculate : (i) the velocity acquired and (ii) the distance travelled in 5 s.
Answer» SOLUTION :NA

Discussion

1914.	A light ray incident on aplane mirrorgets reflected fromit. Another plane mirror is placed suchthat thereflected ray from the first mirror is incident on it If thereflected ray from thesecond mirror travels perpendicular to theindecent ray on the first mirror,determine the angle between two plane mirrors.
Answer» Solution :(i) Angle of incidence = angle of reflection Sum of the three angles of a triangle = `180^(@)` Draw THERAY diagram and DETERMINE the sum of the angle of incidences ANDANGLE of reflections ` 45^(@)`

Discussion

1915.	A particle moving with constant acceleration of 2m/s^(2) due west has an initial velocity of 9 m/s due east. Find the distace covered in the fifth second of its motion.
Answer» Solution :Initial velocity u = +9 m/s Acceleration a = - 2 m/`s^(2)` In this problem, acceleration.s direction is opposite to the velocity.s direction. Let .t. be the TIME taken by the particle to reach a point where it makes a turn along the straight LINE. wehave , V = u + at O = 9 - 2 t We get , t = 4.5s Now let us find the distace convered in `(1)/(2)` second i.e. from 4.5 to 5 second Let u at t = 4.5 sec. Then distance convered in `(1)/(2) ` s. ` s= (1)/(2) at^(2)` s `= (1)/(2) xx 2 xx [ (1)/(2)]^(2)` `= (1)/(4)` m TOTAL distance COVERED in fifth second of its motion is given by `S_(0) = 2s = 2 ((1)/(4)) = (1)/(2) `m .

Discussion

1916.	The mirror used in search light is ....................... .
Answer» SOLUTION :CONCAVE MIRROR

Discussion

1917.	The Quill's tube with its open end upwards is fixed in slanting position making 45^(@)' with the vertical line. If the atmospheric pressure be equal to 'H' and the length of the mercury pallet in the Quill's tube 'h', then the pressure of air enclosed in the tube is equal to _____
Answer» H+h H-h `H+(h)/(SQRT(2))` `H-(h)/(sqrt(2))` ANSWER :C

Discussion

1918.	X represents kerosene and Y represents water Among A and B, which is the right figure? Why? .
Answer» ANSWER :B is TH eright figure.Reason: Density of water is greater than that of kerosene. When taken in the same container due to the DIFFERENCE in density, water comes to the lower PART and kerosene to the upper part.

Discussion

1919.	What type of force is involved in the formation of tides in the sea ?
Answer» Answer :Gravitational FORCE (EXERTED MAINLY by the moon and to some extent by the SUN)

Discussion

1920.	A galvanometer used to detect the flow of current through a circuit should be placed in such a way that the axis of its coil is along the east-west direction. Explain.
Answer» Solution :The bar of diamagnetic materials aligns perpendicular to the magnetic field. The bar of PARAMAGNETIC and ferromagnetic materials aligns in the DIRECTION of the M.F. THIN bar in figure A is made up of diamagnetic, in figure 'C', made up of ferromagnetic substance and in figure B and D , made up of paramagnetic substance.

Discussion

1921.	What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
Answer» Solution :The WORK done by the force of GRAVITY on a satellite moving round the earth is ZERO. The force of gravity acts on the satellite ALONG the radius of its orbit, while the displacement is along the tagent to the orbit at any point. Thus the force is perpendicular to the displacement. Hence, the work done on the satellite is zero.

Discussion

1922.	The values of current I flowing through a resistor for various potential differences V across the resister are given below. What is the value of resistor?
Answer» Solution :Resistance `(R )= triangleV"/"TRIANGLEI` `=10.2-6.7"/"3-2 = 3.5"/"1` `R= 3.5 OMEGA`.

Discussion

1923.	The relation to find speed, frequency and wave length is______.
Answer» ANSWER :`U= LAMBDA UPSILON`

Discussion

1924.	On what factors does the electrostatic force between two charges depend?
Answer» Solution :The electrostatic FORCE between two charges depend on the FOLLOWING FACTORS : (i) VALUE of charges on them. (II) distance between them (iii) nature of medium between them.

Discussion

1925.	Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 km/hr
Answer» Solution :KINETIC energy, `E_(k) = 1/2 mv^(2)` Where, Mass of car, m = 1500 kg VELOCITY of car, v = 60 km/h = `60 xx 5/18 ms^(-1)` Therefore Ek = `1/2 xx 1500 xx (60 xx 5/18)^(2)` =`20.8 xx 10^(4) J`. Hence, `20.8 xx 10^(4)` J of work is REQUIRED to stop the car.

Discussion

1926.	When a ball is lifted to a height of high h, when it is dropped just before touching the ground, what would be the kinetic energy acting on the ball.
Answer» SOLUTION :mgh., According to the conservation of ENERGY potential energy is converted into kinetic energy just above the GROUND. Just before TOUCHING the ground the kinetic energy of the body is equal to mgh.

Discussion

1927.	What is meant by magnification? Write its expression. What is its sign for real image and virtual image?
Answer» Solution :Magnification produced by a SPHERICAL mirror gives how many TIMES the image of an object is magnified with RESPECT to the object size. It can be defined as the ratio of the height of the image `(h_i)` to the height of the object `(h_o)`. Magnification `= m = ("height of the image")/("height of object")` (a) for real image it is NEGATIVE. (b) for VIRTUAL image it is positive.

Discussion

1928.	What do you know about pitch of screw gauge ?
Answer» Solution :Pitch of the screw GAUGE is the DISTANCE between TWO SUCCESSIVE screw threads. It is measured by the RATIO of distance travelled on thepitch scale to the number of rotations of the head scale .

Discussion

1929.	The given below dates are tabulated by Gokul while conducting an experiment to prove Archismedes principles.Fill the missing parts. .
Answer» ANSWER :`450 N``30 N``80 N``20 N`

Discussion

1930.	When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remain the same. Do you hear echo sound on a hotter day ?
Answer» Solution :The SPEED of sound increases on a hotter day (when the temperature is high) and it requires a LARGER distance from the reflecting surface for the eacho to be hard. Since the distance between the reflecting surface and the SOURCE of sound remains the same, no echo can be heard on a hotter day.

Discussion

1931.	Tabulate some situations in your daily life where bouyant forces are experienced in liquids and gases.
Answer» ANSWER :A hydrogen FILLED balloon RISES in the air.Ships floats on the SUFACE of WATER.

Discussion

1932.	If the velocity of a body is double its kinetic energy.
Answer» GETS double BECOMES half does not CHANGE becomes 4 times Answer :D

Discussion

1933.	What is energy?
Answer» SOLUTION :ENERGY is the MEASURE of system.s ABILITY to do WORK.

Discussion

1934.	The power of a water pump is 2 kW. How much amount of water can it raise in 1 minute to a height of 10 m? (Take g=10ms^(-2)).
Answer» SOLUTION :POWER `P=(W)/(t)=(mgh)/(t)` `THEREFORE 2000=(mxx10xx10)/(60)therefore m=1200kg`

Discussion

1935.	The ultimate source of energy is
Answer» wood wind water sun Answer :D

Discussion

1936.	When an object is falling freely from the height h from the earth's surface its gravitational potential energy decreases gradually but its mechanical energy does not change.
Answer» Solution :Because, the gravitational potential ENERGY of the OBJECT at HEIGHT from the earth.s surface is mgh. Now, when the object starts falling freely its height h from the earth.s surface decreases gradually. Hence, its gravitational potential energy goes on decreasing. But, as the freely falling object performs constant accelerated MOTION `(a=g)` in downward direction its velocity goes on increasing uniformly. Hence as per the formula `E_(k)=(1)/(2)mv^(2)` its KINETIC energy goes on increasing. Now, as per the law of conservation of mechanical enregy `deltaE_(k)=-DeltaE_(p)`, the kinetic energy goes on increasing in proportion to the decrease in potential energy. Hence as per the formula `E=E_(p)+E_(k)`, the mechanical energy of the object does not change.

Discussion

1937.	The radius of a press cylinder in a hydraulic press is double the diameter of the pump cylinder. Then
Answer» MECHANICAL ADVANTAGE is 16. the WORK done on the load is EQUAL to the work done by the effort. mechanical advantage is 4 Both (a) and (B) Answer :D

Discussion

1938.	A battery lights a bulb. Describe the energy changes involved in the process.
Answer» SOLUTION :The battery CONVERTS CHEMICAL energy into electrical energy. The electrical energy is TRANSFORMED into heat and LIGHT energy in the bulb.

Discussion

1939.	The wavelength of light of a particular colour is 5800 Å. Express it in. (i) nanometre and (ii)metre
Answer» SOLUTION :`5.8xx10^(-7) m`

Discussion

1940.	A balloon filled with helium gas floats in a big closed jar which is connected to an evacuating pump. What will be your observation, if air from jar is pumped out? Explain your answer.
Answer» Answer :OBSERVATION: The balloon will sink. Explation : As AIR is jumped out from JAR, the density of ari in jar decreases, so the UPTHRUST on balloon decreases. As weight of balloon EXCEEDS the upthrust on it, it sinks.

Discussion

1941.	A block of wood is so loaded it just floats in water at room temperature. What change will occur in the state of floatation, if a. some salt is added to water b.water is heated? Give reason
Answer» ANSWER :a. Floata with some PART outside water B. SINKS

Discussion

1942.	A block of wood floats on water with 2/5 th of its volume above the water surface. Calculate the density of wood.
Answer» SOLUTION :Let the volume of block be V and density of wood be `rho`. Volume of block above the surface of water `=2/5V` `:.` Volume of block immersed `v=V-2/5V=3/5V` By the PRINCIPLE of floatation Weight of the block `=` Weight of water DISPLACED by the immersed part of block i.e. `Vxxrhoxxg=3/5Vxx1xxg` `rho=3/5=0.6gcm^(-3)` (Here the density of water is taken as `1gcm^(-3)`)

Discussion

1943.	A football and a stone has same mass
Answer» Both have same inertia Both have same MOMENTUM Both have DIFFERENT inertia Both have different momentum ANSWER :A

Discussion

1944.	In which mode of transfer of heat molecules pass on heat energy to neighbouring without actually moving from their positions?
Answer» Radiation Conduction CONVECTION Both B and C ANSWER :B

Discussion

1945.	The height of 'Jog fall' in Karnataka state is 250 m high. 2000 ton water per minute falls from it. If this entire energy is used up, then find out the power. (Take g=10ms^(-2))
Answer» <P> Solution :Power `P=(W)/(t)=(mgh)/(t)` `=(2xx10^(6)xx10xx250)/(60)` `=(2)/(3)xx10^(7)W`

Discussion

1946.	A force acts of 0.2 sec on an object having mass 1.4 kg initially at rest. The force stops to act but the object moves through 4m in the next 2 seconds find the magnitude of the force ?
Answer» SOLUTION :14N `(AS_(1))`

Discussion

1947.	A man is kidnapped, blindfolded and imprisoned in a big room. How could the man tell if he was in: (a) a city (b) a village (c) a bare room (d) a furnished room?
Answer» Answer :(a) LOT of noise of heavy traffic in a city (b) Very LITTLE noise of traffic in a village (c) ECHOES of persons talking in a bare roon (d) FURNISHED ROOM is less echoey

Discussion

1948.	What is the actual shape of the orbit of a planet around the sun ? What assumption was made by Newton regarding the shape of an orbit of a planet around the sun for deriving his inverse square rule from Kepler's third law of planetary motion ?
Answer» ANSWER :ELLIPTICAL ; That the ORBIT of a planet around the SUN is 'circular'

Discussion

1949.	The maximum speed of vibrations which produce audible sound will be in:
Answer» DRY air sea water ground glass human blood Answer :C

Discussion

1950.	A microscope has its main scale with 20 divisions in 1 cm and vernier scale with 25 divisions, the length of which is equal to the length of 24 divisions of main scale. The least count of microscope is :
Answer» 0.002 CM 0.001 cm 0.02 cm 0.01 cm Solution :0.002 cm

Discussion

Explore topic-wise InterviewSolutions in .

A porter lifts a luggage of 15 kg from the ground and puts it on his head 1.5 m above the ground. Calculate the work done by him on the luggage.

Express the relationship between the C.G.S. and S.I. units of density.

What are the two factors that influence buoyancy.

Complete the following: 1 m = .............. Å

Four men lift a 250 kg box to a height of 1 m and hold it without raising or lowering it. (i) How much work is done by men in lifting the box? (ii) How much work is done in just holding it? (Take g=10ms^(-2)).

A body floats in a liquid A of density rho_(1) with a part of it submerged inside liquid while in liquid B of density rho_(2) totally submerged inside liquid. The densities rho_(1) and rho_(2) are related as :

On increasing the resistance in a circuit, the current in it:

We come across various activities which we normally consider to be work in day-to-day life. for each of these activities, ask the following questions and answer them : Who (What) is doing work?

We come across various activities which we normally consider to be work in day-to-day life. for each of these activities, ask the following questions and answer them : What is happening to the object?

We come across various activities which we normally consider to be work in day-to-day life. for each of these activities, ask the following questions and answer them : What is the work being done on?

A body, initially at rest, starts moving with a constant acceleration 2 ms^(-2). Calculate : (i) the velocity acquired and (ii) the distance travelled in 5 s.

A particle moving with constant acceleration of 2m/s^(2) due west has an initial velocity of 9 m/s due east. Find the distace covered in the fifth second of its motion.

The mirror used in search light is ....................... .

The Quill's tube with its open end upwards is fixed in slanting position making 45^(@)' with the vertical line. If the atmospheric pressure be equal to 'H' and the length of the mercury pallet in the Quill's tube 'h', then the pressure of air enclosed in the tube is equal to _____

X represents kerosene and Y represents water Among A and B, which is the right figure? Why? .

What type of force is involved in the formation of tides in the sea ?

A galvanometer used to detect the flow of current through a circuit should be placed in such a way that the axis of its coil is along the east-west direction. Explain.

What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.

The values of current I flowing through a resistor for various potential differences V across the resister are given below. What is the value of resistor?

The relation to find speed, frequency and wave length is______.

On what factors does the electrostatic force between two charges depend?

Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 km/hr

When a ball is lifted to a height of high h, when it is dropped just before touching the ground, what would be the kinetic energy acting on the ball.

What is meant by magnification? Write its expression. What is its sign for real image and virtual image?

What do you know about pitch of screw gauge ?

The given below dates are tabulated by Gokul while conducting an experiment to prove Archismedes principles.Fill the missing parts. .

When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remain the same. Do you hear echo sound on a hotter day ?

Tabulate some situations in your daily life where bouyant forces are experienced in liquids and gases.

If the velocity of a body is double its kinetic energy.

What is energy?

The power of a water pump is 2 kW. How much amount of water can it raise in 1 minute to a height of 10 m? (Take g=10ms^(-2)).

The ultimate source of energy is

When an object is falling freely from the height h from the earth's surface its gravitational potential energy decreases gradually but its mechanical energy does not change.

The radius of a press cylinder in a hydraulic press is double the diameter of the pump cylinder. Then

A battery lights a bulb. Describe the energy changes involved in the process.

The wavelength of light of a particular colour is 5800 Å. Express it in. (i) nanometre and (ii)metre

A balloon filled with helium gas floats in a big closed jar which is connected to an evacuating pump. What will be your observation, if air from jar is pumped out? Explain your answer.

A block of wood is so loaded it just floats in water at room temperature. What change will occur in the state of floatation, if a. some salt is added to water b.water is heated? Give reason

A block of wood floats on water with 2/5 th of its volume above the water surface. Calculate the density of wood.

A football and a stone has same mass

In which mode of transfer of heat molecules pass on heat energy to neighbouring without actually moving from their positions?

The height of 'Jog fall' in Karnataka state is 250 m high. 2000 ton water per minute falls from it. If this entire energy is used up, then find out the power. (Take g=10ms^(-2))

A force acts of 0.2 sec on an object having mass 1.4 kg initially at rest. The force stops to act but the object moves through 4m in the next 2 seconds find the magnitude of the force ?

A man is kidnapped, blindfolded and imprisoned in a big room. How could the man tell if he was in: (a) a city (b) a village (c) a bare room (d) a furnished room?

What is the actual shape of the orbit of a planet around the sun ? What assumption was made by Newton regarding the shape of an orbit of a planet around the sun for deriving his inverse square rule from Kepler's third law of planetary motion ?

The maximum speed of vibrations which produce audible sound will be in:

A microscope has its main scale with 20 divisions in 1 cm and vernier scale with 25 divisions, the length of which is equal to the length of 24 divisions of main scale. The least count of microscope is :