1971 + Interview Questions in Physics in Class 9 Page 13 InterviewSolution

601.	What happens to the force between two objects ? If The distance between the objects is doubled and
Answer» SOLUTION :`(1)/(4)` TIMES Tripled `(1)/(3)^(2) = (1)/(9) ` times

Discussion

602.	Define average power.
Answer» Solution :The AVERAGE power is defined as the TOTAL energy CONSUMED DIVIDED by the total time taken.

Discussion

603.	A body of weight 10 N sinks in water. Weight of the water displaced is 2N. What is the weight of the object in water?
Answer» ANSWER :`8 N`

Discussion

604.	Four motorcars A, B, C and D are moving on a road in the same direction. Their graphs for distance-time are shown in the same graph paper, which of the following state is true ?
Answer» Motorcar A is faster than car c. Motorcar D is the fastest. Motorcar B is faster than car D. Motorcar is slower than car B. Solution :The SLOPE of distance-timerepresents speed. But slope of distance-time GRAPH `= TAN theta` `therefore` The angle formed by the distance time graph of motorcar D with time AXIS (positive x-axis) in anticlockwise DIRECTION is the largest. `therefore `Its slopw `= tan theta`is the highest.

Discussion

605.	Distinguish Between Work and Energy
Answer» SOLUTION :`{:(,"Work",,"ENERGY"),(1.,"Work is the PRODUCT of the force acting on",1.,"The capacity of an object to do work is"),(,"the object and the displcement of the object",,"CALLED enery of that object."),(,"in the direction of the force.",,),(2.,"Work is the effect of energy.",2.,"Energy is the cause of work."):}`

Discussion

606.	A metal box is made up of an alloy of zinc and copper metals. It weighs 302 g and 320 g in liquid of relative density 1.4 and water, respectively. The specific gravities (or relative densities) of copper are 7.4 and 8.9, respectively. Arrange the following steps in a proper sequential order to find massess of metals in the alloy.
Answer» FIND the weight of the BOX in a liquid of relative density 1.4 and water along with the relative densities of zinc and copper from the information given in the problem. Note the METALS present in the metal box. Let the masses and volumes of copper and zinc be `m_(c),m_(z),v_(c)andv_(z)` respectively. The weight (w) and volume (v) of the box would be equal to `m_(c)+m_(z)andv_(c)+v_(m)`, respectively. The density of the alloy used for the box is, `d=((m_(c)+m_(z)))/(v_(c)+v_(z)),` substitute `v_(c)=(m_(c))/(d_(c))andv_(z)=(m_(z))/(d_(z))=((w-m_(c)))/(d_(z))`, find the masses of `m_(c)andm_(z)`. Solution :Note the metals present in the metal box. Collect the DATA related to the specific gravities of zinc and copper from the given problem. CONSIDER the masses and volumes of copper and zinc as `m_(c),m_(z),v_(c)andv_(z)`, respectively, and let the weight (w) and volume (v) of the box be equal to `m_(c)+m_(z)andv_(c)+v_(m)`, respectively. The relative density of liquid is 1.4 and `1.4=(w-302)/(w-320)`. Find the value of 'w' Find the density of alloy, `d=(w)/(w-320)` and this is equal to `(m_(c)+m_(z))/(v_(c)+v_(z))`. substitute `v_(c)=(m_(c))/(d_(c))andv_(z)=(m_(z))/(d_(z))=((w-m_(c)))/(d_(z))`find the masses of `m_(c) and m_(z)`.

Discussion

607.	Find the energy possessed by an object of mass 10kg when it is at a height of 6m above the ground. Given g=9.8ms^(-2).
Answer» SOLUTION :Mass of the object `m=10kg` Displacement (height) `h=6m` Acceleration DUE to GRAVITY `g=9.8ms^(-2)` Potential energy = mgh `=10kgxx9.8ms^(-2)xx6m` `=588J` The potential energy is 588 J.

Discussion

608.	Identify the relation between the first pair and complete the second Momentum : mxxv , Impulse: _____
Answer» ANSWER :`Fxxt`

Discussion

609.	Give the properties of X-rays.
Answer»

Discussion

610.	Which of the following frequency of sound can be generated by a vibrating simple pendulum as well as by the vibrating vocal cords of a rhinoceros?
Answer» 5kHz 25 Hz 10 Hz 15,000 Hz Answer :C

Discussion

611.	Take a piece of thread and tie a small place of stone at one of its ends. Hold the other end of the thread and move the stone to describe a circular path with constant speed. A stone describing a circular path with a velocity of constant magnitude Now, release the thread. Can you tell the direction in which the stone moves after it is released ?
Answer» Solution :When the STONE is released, it moves along a straight LINE tangential to the circular path. By repeating the activity for a few times and RELEASING the stone at different positions of the circular path, CHECK whether the DIRECTION in which the stone moves remains the same or not. Observation: When the stone is released, it moves along a straight line tangental to the circular path.

Discussion

612.	A student with a normal eye observes thereading on a vernier scale usinga magnifying glass of focal length 10 cm. What are theminimum and themaximum distances between thescale and the magnifying glassat which he can read thescale when viewing through themagnifying glass ?
Answer» Solution :(i) What is the least distance of DISTINCT vision of HUMAN eye? What is the minimum distance between an object and a convex lens to obtain the virtual IMAGE? `1/f = 1/V - 1/u` substitute f = 10 cm and v = `infty` to obtain 'u'. (ii) `u_(1) = 7.14` cm `u_(2)` = 10 cm

Discussion

613.	"Sound needs a medium for propagation". Justify with an experiment.
Answer» Solution :Sound needs a material LIKE air, WATER, steel, etc. for its propagation. It cannot travel through vacuum. This can be demonstrated by the Bell-Jar experiment. An electric bell and an airtight glass jar are taken. The electric bell is SUSPENDED inside the airtight jar. The jar is connected to a vacuum pump. If the bell is made to ring, we will be able to HEAR the sound of the bell. Now when the jar is EVACUATED with the vacuum pump, the air in the jar is pumped out gradually and the sound becomes feebler and feebler. We will not hear any sound, if the air is fully removed (if the jar has vacuum).

Discussion

614.	Find the size, nature and position of the image formed when an object of size 1 cm is placed at a distance of 15 cm from a concave mirror of focal length 10 cm.
Answer» Solution :Object distance , `u = -15` cm ( to the left of mirror) Image distance, `V = ?` Focal length, `f = - 10 cm` (concave mirror) Using mirror formula, `(1)/(v) + (1)/(u) = (1)/(f)` `(1)/(v ) + (1)/(-15) = (1)/(-10) rArr (1)/(15) = (-1)/(10)` `(1)/(v) = (-1)/(10) + (1)/(15) = (-3 + 2)/(30)= (-1)/(30)` Thus, image distance, `v = -30`cm (negative sign indicates that the image is on the left side of the mirror). `therefore` POSITION of image is 30 cm in front of the mirror. Since the image is in front of the mirror, it is real and INVERTED. To find the size of the image, we have to calculate the magnification. `m = (-v)/(u) = (-(-30) )/( (-15)) = -2` We KNOW that `m = (h_2)/(h_1)` Here, height of the object `h_1 = 1 ` cm `-2 = (h_2)/(1)` `h_2 = -2 xx 1 =-2` cm The height of image is 2 cm ( negative sign shows that the image is FORMED below the principal axis).

Discussion

615.	The density of water is 1000 kg//m^3 and the density of copper is 8900 kg//m^3. Which of the following statements is incorrect ?
Answer» `(a)=("The DENSITY of a CERTAIN volume of COPPER")/("The density of the same volume of water" )=8.9` `(a)=("The density of a certain volume of copper")/("The density of the same volume of water" )=8.9` `(a)=("The density of a certain volume of copper")/("The density of the same volume of water" )=8.9` `(a)=("The density of a certain volume of copper")/("The density of the same volume of water" )=8.9` Answer :B

Discussion

616.	Certain force acting on a 20 kg mass changes its velocity from 5ms^(-1) "to" 2ms^(1) Calculate the work done by the force.
Answer» Solution :Kinetic energy is given by the expression `(Ek)_(r) = 1/2 mv^(2)` (i) Kinetic energy when the object MOVING with a velocity `5 MS^(-1) (Ek)_(v) = 1/2 xx 20 xx (5)^(2) = 250 J` Kinetic energy when the object was moving with a velocity `2 ms^(-1)` `(Ek)_(2) = 1/2 xx 20 xx (2)^(2) = 40 J`

Discussion

617.	A stone of mass 20g is tied to one end of a strong string by a boy. He make it to revolve on a circular path, then work done by him would be ………… joule.
Answer» ANSWER :ZERO

Discussion

618.	What should an object do to produce sound?
Answer» ANSWER :VIBRATE

Discussion

619.	Name the sounds of the frequencies given below: 10 Hz
Answer» SOLUTION :INFRASONIC

Discussion

620.	A bus starts from village A to 7:00 am and reaches village B at 8:30 am. If the discatnace between the villages A and B is 60 km. Find the average speed of the bus.
Answer» Solution :Here, distance (s) COVERED by the bus = 60 km. Time (t) taken `= 8:30 - 7:00 am` `= 1 (1)/(2)` hour` `= (3)/(2)` hour Average VELOCITY `v = (s)/(t) = (60)/((3)/(2)) = 60 xx (2)/(3) = 40 km H ^(-1)` The average speed of the bus is `40 km h ^(-1).`

Discussion

621.	When will you say a body is in (i) uniform acceleration ? (ii) non-uniform acceleration ?
Answer» Solution :(i) Uniform acceleration : If an object travels in a STRAIGHT line and its velocity CHANGES by equal AMOUNTS in equal INTERVALS of time, then the object is SAID to be in uniform acceleration. (ii) Non-uniform acceleration : If the velocity of the object changes by unequal amounts in equal intervals of time, then the object is said to be in non-uniform acceleration.

Discussion

622.	Gravitational force acts on all objects in proportion to their masses. Why the, heavy object does not fall faster than a light object?
Answer» Solution :All objects fall on ground with constant acceleration, called acceleration due to gravity (in the ABSENCE of air RESISTANCE). It is constant and does not depend upon the mass of an object. Hence, HEAVY object not fall faster than LIGHT objects.

Discussion

623.	A lady pulls a bucket filled with water having mass 10kg from a well 8 m deep in 20s. Calculate work done and power. (g=10ms^(-2))
Answer» ANSWER :800 J, 40 W

Discussion

624.	Find out the reasons for the following. Kerosene floats on water.
Answer» ANSWER :KEROSENE has DENSITY LESS than of WATER.

Discussion

625.	An force 10 N, then its kinetic energy would be zero at maximum height.
Answer» ANSWER :1

Discussion

626.	The stone tied to a thread is suspending from a spring balance. The spring stretched down when the stone was suspended from it. Why?
Answer» ANSWER :EARTH's attraction is the REASON [The earth ATTRACTS all objects towards its centre.This force of attraction is the force of GRAVITY.]

Discussion

627.	The brakes applied to a car produce an acceleration of 6 m s^(-2) in the opposite direction to the motion. If the car takes 2s to stop after the application of brakes, calculate the distance it travels during this time.
Answer» Solution :We have ben GIVEN `a=-6ms^(-2),t=2s` and `v=0ms^(-1)` From :EQ we know that v = u + at. `0=u+(-6ms^(-2)xx2s` or u=12 `ms^(-1)` From Eq. we get `s=ut+1/2at^(2)` `=(12ms^(-1))xx(2s)+1/2(-6ms^(-2))(2s)^(2)` = 24 m - 12 m `=12M` THUS, the car will move 12 m before it stops after the application of brakes. Can you now appreciate why drivers are cautioned to maintain some distance between vehicles while travelling on the road?

Discussion

628.	How is ultrasound used for cleaning ?
Answer» Solution :(a) Inertia and frequency . (b) Provided energy from ULTRASONIC sound . Readily OSCILLATE and VIBRATE to DETACH from the surface.

Discussion

629.	What is reveberation ? How can it be reduced?
Answer» Solution :The REPEATED MULTIPLE reflections of sound in any big enclosed space is known as reverberation. The reverberation can be reduced by covering to ceiling and walls of the enclosed space with sound ABSORBING MATERIALS, such as FIBRE board, loose woolens etc.

Discussion

630.	A setellite goes round the earth in a circular orbit with constant speed. Is the motion uniform or accelerated ?
Answer» SOLUTION :ACCELERATED

Discussion

631.	Can the average speed of an object in motion be zero ?
Answer» SOLUTION :No. The AVERAGE SPEED, being a SCALAR quantity, is ALWAYS positive.

Discussion

632.	An iron block of weight 2N is immersed in three different liquids A,B and C weight of the iron block experienced inside the liquids are labelled in the figure. In which liquid, The iron block experiences more buoyancy? .
Answer» ANSWER :C

Discussion

633.	An iron block of weight 2N is immersed in three different liquids A,B and C weight of the iron block experienced inside the liquids are labelled in the figure. Among these three liquids, which has less density? .
Answer» ANSWER :B

Discussion

634.	An iron block of weight 2N is immersed in three different liquids A,B and C weight of the iron block experienced inside the liquids are labelled in the figure. What is the relation between density of a liquid and bouyancy? .
Answer» ANSWER :As density of the liquid INCREASES, BUOYANCY also increases.

Discussion

635.	The main scale of a vernier callipers is calibrated in mm and 19 divisions of main scale are equal in length to 20 divisions of vernier scale. In measuring the diameter of a cylinder by this instrument, the main scale reads 35 divisions and the 4th division of vernier scale coincides with a main scale division. Findleast count .
Answer» SOLUTION :0.005 CM

Discussion

636.	A body of mas 15 kg undergoes downward displacement of 40 m under the effect of gravitational force. Calculate work done. (Take g=10ms^(-1)).
Answer» ANSWER :6000 J

Discussion

637.	Define reverberation time ?
Answer» SOLUTION :Time interval during which ORIGINAL SOUND APPEARS to prolong.

Discussion

638.	P,Q and r are three capillary tubes. If these are dipped in water. Which factors influence capillary rise? .
Answer» ANSWER :DIAMETER of the TUBE

Discussion

639.	How are the following derived units related to the fundamental units ? watt
Answer» SOLUTION :`KG m^2 s^(-3)`

Discussion

640.	What is necessary for work to be done? Choose the correct statement. (1) Action of force is necessary. (2) Displacement is necessary. (3) Displacement in the direction of force is necessary.
Answer» Statement 1 Statement 2 Statement 3 Statement 1 and 3 ANSWER :A::C::D

Discussion

641.	A device in which the loss of heat due to conduction, convectionand radiation is minimized is _____
Answer» SOLAR cell Solar cooker Thermometer Thermos FLASK ANSWER :D

Discussion

642.	A body weighs W gf in air and W_(1) gf when it is completely immersed in water. Find (i) volume of the body (ii) upthrust on the body. (iii) relative density of material of the body.
Answer» ANSWER :(i) `(W-W_(1))CM^(3)` (II) `(W-W_(1))gf` (III) `(W/(W-W_(1)))`

Discussion

643.	Explain how defects in a metal block can be detected using ultrasound.
Answer» Solution :Defects in metal blocks do not allow ultrasound to PASS through them and they are reflected back. Thisfact is used to detect defects in metal blocks. Ultrasound is passed through ONE end of a metal block and detector are placed on the other end. The DEFECTIVE part of the metal block does notallow ultrasound to pass through it. As a result, it will not be DETECTED by the detector. Hence defects in metal blocks can be detected using ultrasound.

Discussion

644.	A homogeneous block floats on water a. Partly immersed b. completely immersed. In each case state the position of centre of buoyancy B with respect to the centre of gravity G of the block.
Answer» Answer :a. B will lie vertically below G b. B will COINCIDE with G

Discussion

645.	Arrange the following steps in a sequential order to prove the convection in gases. (A) Place a lighted candle below chimnery B and hold a lighted incense stick over chimnery A. (B) The smoke given out by incense stick is sucked in through chimney A and comes out through B. (C) Take a rectangular wooden box and fix with two glass chimneys A and B on the top. (D) The lighted candle heats the air and reduces air pressure near the chimney B. The cold, heavy air washes in through chimney A, sweeping the smoke given out by incense stick. (E) On absorbing heat, the hot air molecules move away from the source of heat and molecules of cold air move towards the source of heat, froming convection currents.
Answer» ABEDC CABDE EDCBA ABCDE Solution :Take a rectangular wooden box with two glass chimneys A and B on the top (c). Place a lighted candle below chimney B and HOLD a lighted incense stick over chimney A (a). The smoke given out by incense stick is sucked in through chimney A and COMES out through B (b). The lighted candel heats the air and reduces air pressure near the chimney B. The cold, heavy air rushes in through chimney A, SWEEPING the smoke given out by incense stick (d). On absorbing heat, the hot air molecules move away from the source of heat and molecules move away from the source of heat and molecules of coldair move TOWARDS the source of heat, forming convection currents.

Discussion

646.	What causes buoyant force (or upthrust) on a boat ?
Answer»

Discussion

647.	A body Eoats in kerosene of density 0.8 xx 10^3kg//m^2up water of dersity 1.0 10^3 kg//m^2 , will it sink more or less ? Give reason for your answer.
Answer» Answer :The body will sink less in water ; This is because the DENSITY of water `(1 XX 103 kg//m^2) ` is more than the density of kerosene (0.8 x 103 kg/m3) due to which water will exert a greater 'upward' BUOYANT FORCE on the body

Discussion

648.	What are the three scales of temperature ?
Answer» Solution :There are THREE scales of temperature. (i) Fahrenheit SCALE (ii) CELSIUS or CENTIGRADE scale (iii) Kelvin or Absolute scale.

Discussion

649.	Give the properties of cathode rays.
Answer»

Discussion

650.	What is displacement of an object in motion in unit time called ?
Answer» SOLUTION : VELOCITY

Discussion

Explore topic-wise InterviewSolutions in .

What happens to the force between two objects ? If The distance between the objects is doubled and

Define average power.

A body of weight 10 N sinks in water. Weight of the water displaced is 2N. What is the weight of the object in water?

Four motorcars A, B, C and D are moving on a road in the same direction. Their graphs for distance-time are shown in the same graph paper, which of the following state is true ?

Distinguish Between Work and Energy

Find the energy possessed by an object of mass 10kg when it is at a height of 6m above the ground. Given g=9.8ms^(-2).

Identify the relation between the first pair and complete the second Momentum : mxxv , Impulse: _____

Give the properties of X-rays.

Which of the following frequency of sound can be generated by a vibrating simple pendulum as well as by the vibrating vocal cords of a rhinoceros?

A student with a normal eye observes thereading on a vernier scale usinga magnifying glass of focal length 10 cm. What are theminimum and themaximum distances between thescale and the magnifying glassat which he can read thescale when viewing through themagnifying glass ?

"Sound needs a medium for propagation". Justify with an experiment.

Find the size, nature and position of the image formed when an object of size 1 cm is placed at a distance of 15 cm from a concave mirror of focal length 10 cm.

The density of water is 1000 kg//m^3 and the density of copper is 8900 kg//m^3. Which of the following statements is incorrect ?

Certain force acting on a 20 kg mass changes its velocity from 5ms^(-1) "to" 2ms^(1) Calculate the work done by the force.

A stone of mass 20g is tied to one end of a strong string by a boy. He make it to revolve on a circular path, then work done by him would be ………… joule.

What should an object do to produce sound?

Name the sounds of the frequencies given below: 10 Hz

A bus starts from village A to 7:00 am and reaches village B at 8:30 am. If the discatnace between the villages A and B is 60 km. Find the average speed of the bus.

When will you say a body is in (i) uniform acceleration ? (ii) non-uniform acceleration ?

Gravitational force acts on all objects in proportion to their masses. Why the, heavy object does not fall faster than a light object?

A lady pulls a bucket filled with water having mass 10kg from a well 8 m deep in 20s. Calculate work done and power. (g=10ms^(-2))

Find out the reasons for the following. Kerosene floats on water.

An force 10 N, then its kinetic energy would be zero at maximum height.

The stone tied to a thread is suspending from a spring balance. The spring stretched down when the stone was suspended from it. Why?

The brakes applied to a car produce an acceleration of 6 m s^(-2) in the opposite direction to the motion. If the car takes 2s to stop after the application of brakes, calculate the distance it travels during this time.

How is ultrasound used for cleaning ?

What is reveberation ? How can it be reduced?

A setellite goes round the earth in a circular orbit with constant speed. Is the motion uniform or accelerated ?

Can the average speed of an object in motion be zero ?

An iron block of weight 2N is immersed in three different liquids A,B and C weight of the iron block experienced inside the liquids are labelled in the figure. In which liquid, The iron block experiences more buoyancy? .

An iron block of weight 2N is immersed in three different liquids A,B and C weight of the iron block experienced inside the liquids are labelled in the figure. Among these three liquids, which has less density? .

An iron block of weight 2N is immersed in three different liquids A,B and C weight of the iron block experienced inside the liquids are labelled in the figure. What is the relation between density of a liquid and bouyancy? .

A body of mas 15 kg undergoes downward displacement of 40 m under the effect of gravitational force. Calculate work done. (Take g=10ms^(-1)).

Define reverberation time ?

P,Q and r are three capillary tubes. If these are dipped in water. Which factors influence capillary rise? .

How are the following derived units related to the fundamental units ? watt

What is necessary for work to be done? Choose the correct statement. (1) Action of force is necessary. (2) Displacement is necessary. (3) Displacement in the direction of force is necessary.

A device in which the loss of heat due to conduction, convectionand radiation is minimized is _____

A body weighs W gf in air and W_(1) gf when it is completely immersed in water. Find (i) volume of the body (ii) upthrust on the body. (iii) relative density of material of the body.

Explain how defects in a metal block can be detected using ultrasound.

A homogeneous block floats on water a. Partly immersed b. completely immersed. In each case state the position of centre of buoyancy B with respect to the centre of gravity G of the block.

What causes buoyant force (or upthrust) on a boat ?

A body Eoats in kerosene of density 0.8 xx 10^3kg//m^2up water of dersity 1.0 10^3 kg//m^2 , will it sink more or less ? Give reason for your answer.

What are the three scales of temperature ?

Give the properties of cathode rays.

What is displacement of an object in motion in unit time called ?