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1851.

Can you find the diameter of a thin wire of length 2 m using the ruler from your instrumentbox ?

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Solution :Yes, first you have to wound the WIRE around the scalefor 10 cm and count the number of TURNS in it . Then if you divide 10 cm by number of turns which gives the thickness of the wire.
Discussion
1852.

Complete the following sentence : When sound travels in a medium, the particles of medium .............. but the disturbance ………………….. .

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SOLUTION :do not MOVE, MOVES AHEAD
Discussion
1853.

Name the principle on which a soundboard works.

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ANSWER :REFLECTION of SOUND
Discussion
1854.

When light travels from rarer to denser medium, the refracted ray is _______ the normal.

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SOLUTION :TOWARDS NORMAL
Discussion
1855.

Match the following Column-I Column-II 1. Electric Charge (a) ohm 2. Potential difference (b) ampere 3. Electric field (c ) coulomb 4. Resistance (d) newton per coulomb 5. Electric current (e ) volt.

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SOLUTION :1-C,2-E,3-D,4-A,5-B
Discussion
1856.

Among the following statements, find the wrong one.

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The presence of any IMPURITIES (dissolved) raises the boiling POINT of the SOLUTION.
The boiling point of a solution is always lesser than that of the pure solvent.
The boiling point of an AQUEOUS solution of common salt is always greater than `100^(@)C` at normal atmospheric pressure.
Both (1) and (3) are ture

Solution :Impurities increase the boiling point of a GIVEN solvent.
Discussion
1857.

A 10 kgball is dropped from a height of 10m. Find (a) the initial potential energy of the ball. (b) the kinetic energy justbefore it reaches the ground, and (c ) the speed just before it reaches the ground.

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SOLUTION :980J, 980J, 14m/s
Discussion
1858.

The insulator of electricity is :

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copper
acidulated water
human body
silk
Discussion
1859.

Measure the time it takes you to walk from your house to your bus stop or the school. If you consider that your average walking speed is 4 km h&(-1)estimate the distance of the bus stop or school from your house.

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Solution :it takes 15 minute to REACH the school.
15 minute = 15 `xx` 60 = 900 s
Average WALKING speed is 4 km`h^(-1)` `= (4 xx 1000 m)/(60 xx 60 s) `
Speed `= ("Distance")/("Time")`
`therefore` Distance Speed `xx` Time
`= (4 xx 1000)/(60 xx 60) xx 900 m`
`= 1000 m = 1km`
The school is at a distance of 1 km from your house.
NOTE: To convert `km h ^(-1)` into `ms ^(-1),` multiply it by `(5)/(18).`
Discussion
1860.

What is the relation between mass and weight of a body ?

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Discussion
1861.

Find the thickness of a five rupee coin with the screw gauge. If the pitch scale reading is 1 mm and its head scale coincidence is 68 .

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Solution :Given:pitch SCALE reading = 1 m m
Head scale coincidence = 68
The THICKNESS of a fire RUPEE coin = PSR + HSC `xx` L.C `pm`ZE
` 1 m m + 68 xx 0 . 01 m m `
`= 1 m m + 0 . 68 m m `
= 1 . 68 m m
Discussion
1862.

When two solids areput in two pans of a beam balance, they exactly balance each other in air. When the two solids are completely immersed in water alongwith pans of balance, then they no longer balance each other. Which of the following is the incorrect statement about these balls?

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they have EQUAL masses in air
they have equal WEIGHTS in air
they have equal volumes in air
they have UNEQUAL densities

Answer :C
Discussion
1863.

Assertion (A): Food can be cooked faster in copper bottom vessels Reason (R): Copper is the best conductor of heat.

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If both ASSERTION and REASON are true and reason is the correct EXPLANATION of assertion.
If both assertion and reason are true butreason is not the correct explanation of assertion.
If assertion is true but reason is FALSE
If assertion is false but reason is true

Answer :A
Discussion
1864.

Differentiate between scalar and vector quantities, giving two examples of each.

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Solution :SCALARS : DISTANCE , work MASS .
Vectors : VELOCITY ,acceleration RETARDATION.
Discussion
1865.

A student notes down the observations in the two spring balances and the measuring cylinder. .

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64 cc
36 cc
30 cc
100 cc

Solution :( c) LOSS in weight of the solid = difference in two readings of spring balance `= 65 G - 35 g - 30 g`
Volume of water DISPLACED `= cc (as 1 cc of water weights 1 g)`
Volume of the solid `= 30 cc`.
Discussion
1866.

Refractive index of glass relative to water is 9/8. What is the refractive index of water relative to glass? (AS_(1))

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ANSWER :`8//9`
Discussion
1867.

What is the speed of an apple dropped from a tree after 1.5 second? What distance will it cover during this time? Take g=10 m//s^(2) (AS_(1))

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SOLUTION :`15 m//s, 11.25 m`
Discussion
1868.

Why are knives sharp ?

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Solution :To increase the PRESSURE, AREA is reduced, As pressure `alpha` 1/ Area, hence the pressure or force EXERTED on a body INCREASES.
Discussion
1869.

A women does 250 J of work in 10 seconds and a boy does 100 J of work in 4 seconds. Who delivers more power ?

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Solution :POWER, P = W/t
Power delivered by woman = 250/10 = 25W
Power delivered by boy = 100/4 = 25 W
Both woman and boy DELIVER same power. That is RATE of doing the work by woman and boy are equal.
Discussion
1870.

In thefiguregiven abovethe main scaleis markedin inches.Determinethe length ofthe object heldbetweenthe twoblocks. If 1 inch =2.54 cm ,find the length in cm.

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SOLUTION :`(i) (("relative DENSITY ")_(A))/(("relative density)_(B)) =(M_(A)//V_(A))/(M_(B)//V_(B))`
(ii) `2:3`
Discussion
1871.

If a ray of light passes obliquely from one medium to another, it does not suffer any deviation.

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Solution :FALSE.
Correct Statement: When LIGHT travels from one medium to another, it SUFFERS DEVIATION.
Discussion
1872.

An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object?

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Solution :The WORK done by the FORCE of GRAVITY on the object is zero. This is because the force of gravity acts vertically in the DOWNWARD direction and the DISPLACEMENT of the object is in the horizontal direction.
Discussion
1873.

A car of 1000kg moves with a velocity 20m//s. On applying brakes it comes to rest in 5s. What is the final momentum?

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ANSWER :END MOMENTUM = MV
`100xx0`
= `0 m/s`
Discussion
1874.

A uniform metallic rod AB of length 1.4 m is lifted by two forces P and Q acting along the directions as shown in the figure. If the magnitudes of P and Q are 20 N and 50 N, respectively,find the magnitude and the position of the resultant normal force that acts on the rod.

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Solution :The component of P along normal to AB at A = 20 `cos 60^(@)`= 10 N
The component of Q normal to AB at B = 50 cos `60^(@)` = 25 N. THUS, the given situation is similar to that shown in the figure.

Now applying the principle of moments, we GET
`10(AO)=25(BO)`
` 10 (AO)=25(140-AO)`
`rArrAO=100cm` and MAGNITUDE of
` R=10N+25N=35N`
Discussion
1875.

At a distance L= 400m away from the signal light,brakes are applied to a locomotive movingwith a velocity, u = 54 km/h.Determine the position of rest of the locomotive relative to the signal light after 1 min of the application of the brakes if its acceleration a = - 0.3 m/s^(2)

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Solution :Since the LOCOMOTIVE moves with a constant deceleration after the application of brakes, it will come to rest in .t. sec . We KNOW ,
v = U + at
Here u = 54 km/h = 54 x 5/18 = 15 m/s
Let v = 0 at time .t. and given
a = - 0.3 m/`S^(2)`
From v = u + at we GET t= `(v - u)/(a)`
We get , t `= (-15)/(-0.3) = 50 s `
During which it will cover a distance
s = - `(u^(2))/(2a)`
`= - (15^(2))/(2 xx (-0.3))`
= `(225)/(0.6)`
= 375 m
Thus in 1 min after the application of brakesthe locomotive will be at a distance l = L – s = 400 – 375 = 25 m from the signal light.
Discussion
1876.

The work done on the object is negative, then the measure of angle between force and displacement would be …………

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`0^(@)`
`45^(@)`
`90^(@)`
`180^(@)`

ANSWER :A
Discussion
1877.

Which of the following is true for displacement ? (a) It cannot be zero. (b) Its magnitude is greater than the distance travelled by the object.

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Only A
Only B
Both A and B
None of these

Answer :D
Discussion
1878.

Difine least count of any device .

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Solution :LEAST COUNT is the least distance MEASURED in a given DEVICE by it .
Discussion
1879.

Complete the following sentences: Density in kgm^(-3)= ………xx density in gcm^(-3)

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ANSWER :1000
Discussion
1880.

The coin remain at rest shown in the fig. This is due to

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Inertia of rest
two forces act on the coin which balance each other
No unbalanced FORCE ACTS on it
all of these

Answer :D
Discussion
1881.

In the setp up shown the weight of the body was measured in air and in water. The reading of mark X in the spring balance would be:

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`36G wt`
`30 G wt`
`24 g wt`
`6 g wt`

ANSWER :C
Discussion
1882.

The time period of a simple pendulum is 2 s. What is its frequency ? What name is given to such a pendulum ?

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SOLUTION :`0.5 s^(-1)` SECONDS. PENDULUM.
Discussion
1883.

Distinguish BetweenPotential energy and Kinetic energy

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Solution :`{:("Potential energy","kinetic energy"),("1. The energy possessed by an object on account","1. The energy possessed by an object due to "),("of its SPECIFIC state or position is called its","its MOTION is called its kinetic energy."),("potential energy.",),("2.It occurs in VARIOUS forms such as gravitational","2. It occurs only in one form and for doing" ),("potential energy and electric potential energy"," WORK it does not have to be TRANSFORMED"),("but work is not done till it is transformed","into another form."),("into kinetic energy.",):}`
Discussion
1884.

Conduction process can be explained on the basis of both atomic model and kinetic model.

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ANSWER :TRUE
Discussion
1885.

The absolute refractive index of water is 4/3. What is the critical angle? (AS_(1))

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ANSWER :`48.5^(@)`
Discussion
1886.

An object of mass 15kg is moving with a uniform velocity of 4ms^(-1). What is the kinetic energy possessed by the object?

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SOLUTION :MASS of the object `m=15kg`, Velocity of the object `v=4ms^(-1)`
`E_(k)=(1)/(2)mv^(2)`
`=(1)/(2)xx15kgxx(4ms^(-1))^(2)`
`=120J`
The kinetic energy of the object is 120 J.
Discussion
1887.

Figure shows the distance-time graph of three object A, B and C. Study the graph and answer the following questions : (a) Which of the three is travelling the fastest ? (b) Are all three ever at the same point on the road ? ( c) How far has C travelld by when B passes A ? (d) How far has B travelled by the time it passes C ?

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Solution :(a) The slope of distance-time graph of a moving object indicates its speed. Greater the slope, higher is the speed. Now, in the given FIGURE, the slope of distance-time graph of object B is the maximum, sothe object B is travelling the fastest.
(b) In order to be at the same point on the road, the respective distance and time values for all the three moving OBJECTS should be the same. Since the distance-time graph lines of the three objects A, B and C do not cross at a SINGLE point, THEREFORE, the three objects are never at the same point on the road.
(c) We can see from the given figure that when B passes A at point D, then the C is at point E. If we LOCATE the distance corresponding to point E on the Y-axis, we find that it is 6.5km. Thus, C hastravelled 6.5 km when B passes A.
(d) The distance-time graphs of B and C meet at point F. If we locate the distance corresponding to point F on the Y-axis, we will find that it is 5 km. Thus, B has travelled 5 km by the time it passes C.
Discussion
1888.

How can the speed of rotation of a coil be increased? Write at least three methods.

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Solution :The SPEED of ROTATION of a coil can be increased by
(i) increasing the strength of the current in the coil
(II) increasing the AREA of the coil
(iii) increasing the strength of the magnetic field.
Discussion
1889.

A car weighing 1000 kg is travelling at the speed of 15ms^(-1). It decelerated due to brakes applied and stops after covering a distance of 25 m. Find the force exerted by the brakes and the work done by the brakes.

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Solution :Here, `m=1000kg,u=15ms^(-1),v=0,`
`s=25m`
`v^(2)-u^(2)=2as`
`therefore 0-(15)^(2)=2axx25`
`therefore -225=50alpha`
`therefore a=-(225)/(50)=-4.5ms^(-2)`
Negative acceleration means DECELERATION.
`therefore` Deceleration `=4.5ms^(-2)`
Decelerating FORCE `F=ma`
`=1000kgxx4.5ms^(-2)`
`=4500 N`
WORK done by the brakes,
`W=Fs`
`=4500kgxx25m`
`=112500J`
Discussion
1890.

A submarine emits a sonar pulse, which returns from an underwater cliff in 1.02s.If the speed of sound in salt water is 1531 m/s , how far away is the cliff ?

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Solution :Time TAKEN by the sonar pulse to return `t=1.02s`.
speed of sound in SALT WATER, `v=1531m//s`
Distance of the CLIFF from the submarine
`=` speed of Sound `xx` Time taken.
Distance of the cliff from the submarine
`=1.02xx1531=1561.62m`
Distance travelled by the sonarpulse during its TRANSMISSION and reception in water `=2xx` Actual distance `=` 2d, Actual distance d `=` Distance of the cliff from the submarine /2
`=1561//2=780.31m`
Discussion
1891.

Certain force acting on a 20 kg mass changes its velocity from 5m/s to 2m/s calculate the work done by the force.

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SOLUTION :Given mass of the object (m) 20 kg
Initial velocity of the object (u) = 5 m/s
FINAL velocity of the object (v) = 2 m/s
According to work energy theorem, W = `1/2 mv^(2) - 1/2 mu^(2)`
Therefore = `1/2 xx 20g xx (2^(2) - 5^(2)) = 10 xx (4 - 25) = (10 xx -21)` W = -210 J
Discussion
1892.

Under what conditions, do gases become conductors of electricity?

Answer»
Discussion
1893.

An electric bulb of 60 W is used for 10 h per day ………….. Unit of electrical energy will be used in the month of June.

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ANSWER :18
Discussion
1894.

Find the time period of the wave whose frequency is 500Hz?

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SOLUTION :from `T=//upsilon= 1//500 s`
`=0.002 s`
Discussion
1895.

{:("Column - I ","Column - II "),("(a) Screw gauge","(i) Vegetables"),("(b) Vernier Caliper","(ii) Coins"),("(c) Beam balance","(iii)Gold ornaments"),("(d) Digital balance","(iv) Cricket ball"):}

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ANSWER :(a) (ii)(B) (iv)(c) (i)(d) (III)
Discussion
1896.

1 metric ton is equal to . . . . . .

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100 QUINTALS
10 quintals
1/10 quintals
1/100 quintals

Answer :A::B
Discussion
1897.

Thefundamentalfrequecy of a stationarywaveformedin astretched wire is n= (1)/(2l) sqrt((1)/(m))wherel is lengthof thevibratingwire'T' is thetensionin thewire and 'm' is itsmas perunitlength . If thepercentage error inmeasurement of l Tand m area% ,b% andc% respectivelythen findthe maximum errorin measuringn.

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SOLUTION :Diameter =x+ly
Here x is theM.S.Rin MM l is theleast countin mm and y is theverniercoincindingdivisionSubstancethe givenvaluesand estimatex and y
In CASEOF ZEROERROR,
Diameter=x+ l(y-z) where z is theV.S.D for positivezeroerror . (correctionis negative)
`(ii) 19,5"" (b) 20,2`
Discussion
1898.

What is the relation between viscosity and temperature?

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ANSWER :As TEMPARATURE INCREASES, VISCOSITY DECREASES.
Discussion
1899.

Roman Numerals

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no load is placed on the hook.
the RIDER is at the ZERO of the SCALE.
Both (a) and (b)
The beam of a ROMAN steelyard can never be horizontal.

Solution :When no load is placed on the hook, the Roman steel yard can be MADE horizontal only by placing rider at the zero of the scale.
Discussion
1900.

"The value of g remains same at all places on the earth surface'. Is this statement true ? Give reason for your answer.

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Solution :No. The VALUE of g is maximum at the POLES and minimum at the EQUATOR on the earth SURFACE.
Discussion