1971 + Interview Questions in Physics in Class 9 Page 28 InterviewSolution

1351.	("1 megawatt (MW)")/("1 kilowatt (kW)")=…………..
Answer» `10^(-3)` `10^(3)` `10^(6)` `10^(-6)` SOLUTION :`(1MW)/(1kW)=(10^(6)W)/(10^(3)W)=10^(3)`

Discussion

1352.	A sound wave has a frequency of 2 kHz and wavelengthof 15 cm. How much time will it take to travel 1.5 km ?
Answer» Solution :Speed, `V=n lambda` Here, `n=2kHz=2000Hz` `lambda=15 CM = 0.15m` `v=0.15 xx 2000=300 ms^(-1)` Time (t) `=("Distance (d)")/("Velocity (v)")` `t=(1500)/(300)=5s` The sound will take 5 s to TRAVEL a distance of 1.5 km.

Discussion

1353.	What do you mean by uniform motion?
Answer» Solution :An OBJECT is SAID to be in uniform motion if it covers equal distances in equal intervals of time how so EVER big or SMALL these time intervals MAY be.

Discussion

1354.	The mass of a body is 30kg.What is its weight on the moon? (g = 1.62m//s^2)
Answer» ANSWER :WEIGHT = MG = `50xx1.62 = 81 N

Discussion

1355.	Which of the following vibrates when a muscial note is produced by the cymbals in an orchestra?
Answer» STRETCHED strings stretched membranes metal plates air columns Answer :C

Discussion

1356.	If the relative density of a liquid is 1, Which is the instrument used for finding relative density.
Answer» ANSWER : HYDROMETER

Discussion

1357.	A trough contains the two immiscible liquids 'A' and 'B' having densities 'p_(A)'and'p_(B)'(p_(B)gtp_(A)). A cylindrical body having uniform area of cross section is immersed completely and vertically in the liquids such that 1//3rd of its length is in liquid 'B' and the remaining is in liquid 'A'. Find the density of the body.
Answer» Solution :Take the volume of cylindrical body as V. Is the cylindrical body completely immersed in both immiscible liquids 'A' and 'B' ? Find the volume of the cylinder immersed in liquid 'A' and also in liquid 'B' by using FORMULA, V=a.h(1) Is this equal to the volume of the DISPLACED liquids of 'A' (or) 'B' ? Now, weight of floating body = weight of the displaced liquids = total UPTHRUST acting on the body. Here, weight of floating body = mg = `Vd_(s)g`(2) `rArr"Then",V.d_(s)g=(2)/(3)V*d_(Axx)g+(1)/(3)Vd_(B)g`(3) Find the DENSITY of the body from equation (3)

Discussion

1358.	The unit of work and energy is the same.
Answer» ANSWER :1

Discussion

1359.	A horse shoe magnet has two iron needles attached at its ends. Show on a diagram the positions occupied by the needles and name the phenomenon which comes into play.
Answer» Solution :Fig.shows the iron needles attached at the ends of a horse SHOE magnet. The lower ends of both the needles GET attracted TOWARDS each other, SINCE they have opposite polarities. The upper ends touching the poles of the magnet, have polarities opposite to that of the magnet. This phenomenon is called MAGNETIC induction.

Discussion

1360.	The velocity of an object increases at a constant rate from 20 m s^(-1) to 50 m s^(-1)in 10 s. Find the acceleration.
Answer» Solution :Given u = 20 m `s^(-1), v = 50 m s^(-1), t = 10 s` Acceleration a = `(v-u)/(t) = (50 m s^(-1)-20 m s^(-1))/(10 s )` or ` a= (30 ms^(-1))/(10 s ) = 3 m s^(-2)`.

Discussion

1361.	The mass of a molecule of hydrogen is 3.332xx10^(-27) kg. Find the mass of 1 kg mol of hydrogen gas.
Answer» Solution :GIVEN : mass of a MOLECULE of hydrogen `=3.332xx10^(-27) KG ` 1 kg mol of hydrogen gas will contain `6.02xx 10^(26)` molecules of hydrogen `therefore` The mass of 1 kg mol of hydrogen gas `= (6.02 xx 10^(26)) xx 3.332 xx 10^(-27) kg` `= 2.0 kg `

Discussion

1362.	The unit of retardation is :
Answer» `m s^(-1)` ` m s^(-2)` m `m s^(2)` SOLUTION :NA

Discussion

1363.	In J.J. Thomson's experiment, the portion of the tube opposite cathode starts glowring due to_______.
Answer»

Discussion

1364.	Theworkingof acommon balance or a physicalbalance is based on the 'Principleof moments. A metre scaleof uniform densityis balanced at thecentre. Ifa massof 2 kgis suspended at anadge of the scale thenwhat mass shouldbe suspended on otherside at 1//4 th length of thescaleto maintainthe horizontal position of thescale ?
Answer» Solution :Least count `=(1M.S.D.)/(N)` ZEROCORRECTION=- zeroerror =- [(MAIN scale COINCIDINGDIVISION) -(V.S. coincidingdivision) (ii) +1.2 mm

Discussion

1365.	What is the other name of a lound-halider?
Answer» ANSWER :MEGAPHONE

Discussion

1366.	What will be the weight of a body at the centre of earth.
Answer» ANSWER :WEIGHT at the CENTRE of EARTH is ZERO.

Discussion

1367.	Whay is the ratio of the charge to mass of the cathode rays ?
Answer»

Discussion

1368.	A boy lifts a mass of 300g for 1.2 second at height of 4m. What would be the power of boy? (Take g=10ms^(-2)).
Answer» <P>`5W` `10W` `15W` `20W` Solution :`P=(W)/(t)` `=(MGH)/(t)` `=((0.3kg)xx(10ms^(-2))xx(4M))/(1.2s)=10W`

Discussion

1369.	Express each of the following in m s^(-1) : (a)1 km h^(-1) (b) 18 km min^(-1)
Answer» SOLUTION :(a) 0.278 `m s^(-1)` (B) 300 `m s^(-1)`

Discussion

1370.	Name the physical quantities of which the units are : (i) volt, (ii) coulomb, (iii) ohm, (iv) ampere.
Answer» Answer :(i) Potential DIFFERENCE (ii) CHARGE (III) RESISTANCE, (iv) current.

Discussion

1371.	A research team sends a sonar signal to confirm the depth of a sea. They heard an echo after 6s.Find the depth of the sea m/s? If the speed of sound in sea water is 1500m/s?
Answer» Solution :LET the depth of the sea = d m Then Total distance travelled by sonar SIGNAL `(s) = 2D` `=1500 m//s` Total time TAKEN `(t) = 6s` From, `s= ut`, `2d=1500 m//s XX 6s` `d=9000//2 m=4.5` km

Discussion

1372.	Find the value of 1 unified atoic mass unit (1u) in kg.
Answer» SOLUTION :`1u=(1)/(12)` of a `C_(12)` isotope. 1ml `""^(12)C=12g""^(12)C` i.e., `N_(A)` number of `""^(12)C=12g` [`thereforeN_(A)`=Avogadro number] `therefore 1u=(1)/(12)XX(1)/(N_(A))xx12g=(1)/(N_(A))g=(1)/(1000N_(A))kg=1.6xx10^(-27)kg`.

Discussion

1373.	(a) What is the frequency range of hearing in humans? (b) Which of the following sound frequencies cannot be heard by a human ear? (i) 10 Hz (ii) 100 Hz (iii) 10,000 Hz (iv) 15Hz (v) 40,000 Hz
Answer» ANSWER :(B) 10HZ; 15HZ; 40,000 HZ

Discussion

1374.	Complete the following: 1 year = ……………… s
Answer» SOLUTION :`3.15xx10^(7)`

Discussion

1375.	The odometer of a car reads 2000 km at the start of a trip and 2400 km at the end of the trip. If the trip took 8 hours, then the average of the car would be ....... km h^(-1).
Answer» SOLUTION :Total distance travelled = (Final observation) -(INITIAL observation) `= 2400 - 2000` `= 400 km` Average speed `= ("Total distance travelled")/("Total time taken") = (400 km)(8h)=50 km h ^(-1)`

Discussion

1376.	We can distinguish between the muscial sounds produced by different signers on the basis of the characteristic of sound called:
Answer» frequency timbre pitch loundness Answer :B

Discussion

1377.	What is inertia ?
Answer» Solution :The natural tendency of an object to resist a CHANGE in their state of rest or of uniform MOTION is CALLED INERTIA.

Discussion

1378.	What type of motion does an athlete moving along a circular path with constant speed execute ?
Answer» SOLUTION :The MOTION EXECUTED by the ATHLETE is ACCELERATED motion.

Discussion

1379.	Analyse the graphs given below. Which graph indicates the motion of freely falling stone?
Answer» ANSWER :GARPH (3)

Discussion

1380.	The odometer of a car reads 2000 km at the start of a trip and 2400 km at the end of the trip. If the trip took 8h, calculate the average speed of the car in kmh^(-1) and ms^(-1).
Answer» Solution :Distance covered by the car, `s = 2400 km - 2000 km = 400 km ` Time elapsed `t = 8` h Average SPEED of the car, `V _(av) = (s)/(t) = (400 km )/(8h)= 50 km h ^(-1)` `= 50 XX (km)/(h) xx (1000m)/(1km) xx (1h)/(3600 s)= 13.9 ms ^(-1)` The average speed of the car is `50 km h ^(-1) or 13.9 m s ^(-1).`

Discussion

1381.	Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60kmh^(-1).
Answer» Solution :Here, `m=1500kg`, `v=60kmh^(-1)=60xx(5)/(18)MS^(-1)=(50)/(3)ms^(-1)`, findla velocity is ZERO. `THEREFORE` Work REQUIRED to stop the car = change in K.E. of the car `=(1)/(2)mv^(2)-(1)/(2)m(0)^(2)` `=(1)/(2)mv^(2)` `=(1)/(2)xx1500xx((50)/(3))^(2)J` `=(1)/(2)xx1500xx(50)/(3)xx(50)/(3)J` `~~208333.3J`

Discussion

1382.	Sound travels in air:
Answer» if there is no moisture in the atmosphere. if PARTICLES of MEDIUM travel from ONE place to another. if both particles as well as DISTURBANCE move from one place to another. if disturbance moves. Answer :B

Discussion

1383.	A body which floated in water sank, when put in kerosene. Why did it happen?
Answer» Answer :Kerosene has LOWER density than water. So kerosene can not exert more BUOYANCY when COMPARED with water.

Discussion

1384.	A car starting from rest acquires a velocity 180 m s^(-1) in 0.05 h. Find the acceleration.
Answer» SOLUTION :NA

Discussion

1385.	While doing an experiment on plotting the temperaure-time graph of hot water as it cools, we can get a good graph:
Answer» only by NOTING the TEMPERATURE of hot water every 30 seconds throughout only by noting the temperature of hot water every 1 MINUTE throughout by noting the temperature of hot water every 1 minute to start with and every 2 minutes later on by noting the temperature of hot water every 2 minutes to start with and every 1 minute later on Answer :C

Discussion

1386.	........... is used as reflectors in torchlight.
Answer» CONCAVE mirror Plane mirror Convex mirror Answer :A

Discussion

1387.	Calculate the work done by a student in lifting a 0.5 kg book from the ground and keeping it on a shelf of 1.5 m height.(g = 9.8 m//s^(2))
Answer» SOLUTION :The mass of the BOOK = 0.5 kg The force of GRAVITY acting on the book is EQUAL to .mg. That is mg ` = 0.5 xx 9.8` ` = 4.9` N The student has to apply a force equal to that of force of gravity acting on the book in order to lift it.

Discussion

1388.	Find the factors affecting the value of g?
Answer» ANSWER :• MASS of the EARTH • RADIUS of the earth

Discussion

1389.	For plotting temperature time graph for a hot body as it cools to room temperature, a student is to choose one each from each of the following pairs. A: Calorimeter (i) blackened from outside (ii) polished from outside B: Base for keeping the calorimeter (i) insulated (ii) metallic In order to get the correct graph he should prefer to choose:
Answer» A (i), B(II) A (ii), B(ii) A (i), B(i) A (ii), B (i) ANSWER :C

Discussion

1390.	When a body is fully immersed in a liquid, the apparent loss in its weght is:
Answer» EQUAL to the weight of the liquid displaced more than the weight of the liquid desplaced less than the weight of the liquid displaced depends UPON the MANNER in which the body is immersed in the liquid. Answer :A

Discussion

1391.	Use the data given in the following table and draw the displacement-time graph for the object : Using the graph, find the average velocity (i) for first 4s (ii) for next 4s and (iii) for last 6 s.
Answer» Solution : (i) For first 4S, average VELOCITY `= 1 ms ^(-1)` (II) For next 4 s, average velocity `=0 ms ^(-1)` (iii) For last 6s, average velocity `= -1 ms ^(-1)`

Discussion

1392.	Calculate the molefraction of each component in a solution made by mixing 34.5 g of methanol (CH_(3)OH) and 40.0 g of H_(2)O.
Answer» SOLUTION :`x_("METHANOL")=0.327,x_("WATER")=0.673`.

Discussion

1393.	X-rays are electromagnetic waves. Justify.
Answer»

Discussion

1394.	X-rays are produced in________.
Answer»

Discussion

1395.	Ina physicalbalance when thebaeamis released withemptypansthesuccessiveleftand rightturningpointsare obtainedas 5,6,6 and18, 18respectively. Afterplacingthe substancewhosemass is tobe determined andwhen thebeam isreleasedtheresting pointobtainedis 13. When 10mg isaddedto thepan theresting pointisobtainedas 11. if themass at LRPis 60g , Findthe correct mass ofthe bodycorrected to amilligram.
Answer»

Discussion

1396.	In an instrument, there are 25 divisions on the vernier scale which have length of 24 divisions of the main scale. 1 cm on main scale is divided in 20 equal parts. Find the least count.
Answer» SOLUTION :The value of one main scale DIVISION x = `1/(20)` CM The number of divisions on vernier scale n=25 `therefore ` L.C. of vernier `=("Value of one main scale division (x)")/("Number of divisions on vernier scale (n)")` `=((1//20)cm)/(25) = 1/(500) cm = 0.002 cm`

Discussion

1397.	If the work done on an object is 10 J and the object is displaced through 2 m, then what is the force applied?
Answer» SOLUTION :`W=Fxxs THEREFORE 10J=Fxx2m therefore F=5N`

Discussion

1398.	Determinethe leastcountand thezeroerror of theverniercalipers shownin thefigurebelow . Whatisthecorresponding zerocorrection?
Answer» Solution :(i) Timeperiodoif a pendulum is proportionalto THESQUAREROOT of ITSLENGTH. (ii) If theclockloses 1 minuteinevery24 hoursdoes itmeanthat the timeperiodis GREATER thantherequriedone thenshouldthe length of thependulum be increasedor decreased

Discussion

1399.	Name two substances which contract on heating.
Answer» ANSWER :WATER from `0^(@)C` to `4^(@)C`

Discussion

1400.	n electrons flow through a cross section of aconductor in time t. If charge on an electron is e, then write an expression for the current inthe conductor.
Answer» ANSWER :`(NE)/(t)`

Discussion

Explore topic-wise InterviewSolutions in .

("1 megawatt (MW)")/("1 kilowatt (kW)")=…………..

A sound wave has a frequency of 2 kHz and wavelengthof 15 cm. How much time will it take to travel 1.5 km ?

What do you mean by uniform motion?

The mass of a body is 30kg.What is its weight on the moon? (g = 1.62m//s^2)

Which of the following vibrates when a muscial note is produced by the cymbals in an orchestra?

If the relative density of a liquid is 1, Which is the instrument used for finding relative density.

The unit of work and energy is the same.

A horse shoe magnet has two iron needles attached at its ends. Show on a diagram the positions occupied by the needles and name the phenomenon which comes into play.

The velocity of an object increases at a constant rate from 20 m s^(-1) to 50 m s^(-1)in 10 s. Find the acceleration.

The mass of a molecule of hydrogen is 3.332xx10^(-27) kg. Find the mass of 1 kg mol of hydrogen gas.

The unit of retardation is :

In J.J. Thomson's experiment, the portion of the tube opposite cathode starts glowring due to_______.

What is the other name of a lound-halider?

What will be the weight of a body at the centre of earth.

Whay is the ratio of the charge to mass of the cathode rays ?

A boy lifts a mass of 300g for 1.2 second at height of 4m. What would be the power of boy? (Take g=10ms^(-2)).

Express each of the following in m s^(-1) : (a)1 km h^(-1) (b) 18 km min^(-1)

Name the physical quantities of which the units are : (i) volt, (ii) coulomb, (iii) ohm, (iv) ampere.

A research team sends a sonar signal to confirm the depth of a sea. They heard an echo after 6s.Find the depth of the sea m/s? If the speed of sound in sea water is 1500m/s?

Find the value of 1 unified atoic mass unit (1u) in kg.

(a) What is the frequency range of hearing in humans? (b) Which of the following sound frequencies cannot be heard by a human ear? (i) 10 Hz (ii) 100 Hz (iii) 10,000 Hz (iv) 15Hz (v) 40,000 Hz

Complete the following: 1 year = ……………… s

The odometer of a car reads 2000 km at the start of a trip and 2400 km at the end of the trip. If the trip took 8 hours, then the average of the car would be ....... km h^(-1).

We can distinguish between the muscial sounds produced by different signers on the basis of the characteristic of sound called:

What is inertia ?

What type of motion does an athlete moving along a circular path with constant speed execute ?

Analyse the graphs given below. Which graph indicates the motion of freely falling stone?

The odometer of a car reads 2000 km at the start of a trip and 2400 km at the end of the trip. If the trip took 8h, calculate the average speed of the car in kmh^(-1) and ms^(-1).

Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60kmh^(-1).

Sound travels in air:

A body which floated in water sank, when put in kerosene. Why did it happen?

A car starting from rest acquires a velocity 180 m s^(-1) in 0.05 h. Find the acceleration.

While doing an experiment on plotting the temperaure-time graph of hot water as it cools, we can get a good graph:

........... is used as reflectors in torchlight.

Calculate the work done by a student in lifting a 0.5 kg book from the ground and keeping it on a shelf of 1.5 m height.(g = 9.8 m//s^(2))

Find the factors affecting the value of g?

When a body is fully immersed in a liquid, the apparent loss in its weght is:

Use the data given in the following table and draw the displacement-time graph for the object : Using the graph, find the average velocity (i) for first 4s (ii) for next 4s and (iii) for last 6 s.

Calculate the molefraction of each component in a solution made by mixing 34.5 g of methanol (CH_(3)OH) and 40.0 g of H_(2)O.

X-rays are electromagnetic waves. Justify.

X-rays are produced in________.

In an instrument, there are 25 divisions on the vernier scale which have length of 24 divisions of the main scale. 1 cm on main scale is divided in 20 equal parts. Find the least count.

If the work done on an object is 10 J and the object is displaced through 2 m, then what is the force applied?

Determinethe leastcountand thezeroerror of theverniercalipers shownin thefigurebelow . Whatisthecorresponding zerocorrection?

Name two substances which contract on heating.

n electrons flow through a cross section of aconductor in time t. If charge on an electron is e, then write an expression for the current inthe conductor.