# 400 - Physics Questions Answers

4 moles of an ideal monoatomic gas is mixed with 6 moles of a non reactive diatomic ideal gas. the molar heat capacity of the mixture at constant volume is (assume no vibration) nearly

(1) 27 J mol‾¹K‾¹

(2) 17 J mol‾¹K‾¹

(3) 7 J mol‾¹K‾¹

(4) 37 J mol‾¹K‾¹

**Asked By: HIMANSHU MITTAL**

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**Joshi sir comment**

at constant volume work done = 0

degree of freedom = 4(3) + 6(5) / 4 + 6 = 12+30/10 = 4.2 so γ = 1 + (2/4.2)

so molar heat capacity = R/(γ-1)

consider an ideal gas contained in a vessel. if the intermolecular interaction suddenly beings to act, which of the following will happen?

(1) the pressure decreases

(2) the pressure increases

(3) the pressure remain unchanged

(4) the gas collapses

**Asked By: HIMANSHU MITTAL**

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**Joshi sir comment**

if the intermolecular interaction suddenly beings to act, then the pressure increases because due to intermolecular interaction gase will work as real gas

in the previous case if north pole is brought near the mettalic ring why the direction is reversed. we have to consider the drn of magnetic field of magnet or not. if yes then which drn N-S or S-N.

**Asked By: NIKHIL VARSHNEY**

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**Joshi sir comment**

The south pole of a magnet is bought near a metallic ring ,the direction induced current in the ring will be? Explain it clearly.

**Asked By: NIKHIL VARSHNEY**

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**Joshi sir comment**

If observer is in the side of magnet, then in the given case form **S** in the ring, it will give you clockwise direction

can you give me an idea of solving the parallel LC circuit? Also to find the phase difference between the I and E?

**Asked By: NIKHIL VARSHNEY**

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**Joshi sir comment**

1st make a 3 line circuit in which ac source, resistor with an inductor and resistor with a capacitor will be there in the three lines then divide total current "I"

from AC into the two legs, equations will be

**e = L di _{1}/dt + i_{1}R (1)**

**e =q _{2 }/ C + i_{2} R (2) here dq_{2} / dt = i_{2}**

now solve

_{ }

Why earth moves in orbital motion around the sun ...? why not in circular motion...?

**Asked By: HARISH**

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**Joshi sir comment**

Since every heavenly body like sun, earth, moon are rotating freely in free space, there is no body which is placed on a base, so rotation of every body depends on all the surrounding bodies. It means its track will also depend on the attraction forces given by all the surrounding bodies.

Two cylinders are twisted by the same external torque.If the ratios of their modulous of rigidity , radii & lengths are 1:2, 2:3 & 3:4 respectively. Then find the ratio of angle of twist ??

**Asked By: AMIT DAS**

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**Joshi sir comment**

Let the angle rotated due to torque = θ and angle of twist (shear) = δ

then arc covered = rθ (here r is radius)

now for twist of wire δ = rθ/l (here l is length)

according to formula η = F/Aδ and torque ζ = kFr (here k is constant of proportion)

we get ζ = kηAδr

Use the formula and get the answer, you have to calculate ratio of δ's so k is not required

how far from earth we can see earth as a whole elliptical?{we can clearly see the earth

**Asked By: SAHIL KUMAR**

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**Joshi sir comment**

for getting the complete vision we should draw tangents at the extreme of major and minor axis of the earth, this will give a point of intersection for which height from centre of earth will be R√2 so height from earth surface will be R√2 - R = R(√2-1)

here R is used for radius of earth

This is approximate calculation only

**Solution by Joshi sir**

for getting the complete vision we should draw tangents at the extreme of major and minor axis of the earth, this will give a point of intersection for which height from centre of earth will be R√2 so height from earth surface will be R√2 - R = R(√2-1)

here R is used for radius of earth

A 20 cm long test tube (cylindrical) is inverted & pushed vertically down into the water . when the closed end is at water surface, how high has the water risen inside the tube? [p atm =10^5 N/m²]

**Asked By: AMIT DAS**

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**Joshi sir comment**

Let the height of water in the tube is x cm. then according to PV = constant, calculate the pressure by (20-x) cm. column

then P_{0} + pressure by 20 cm water = pressure by (20-x) cm. column + pressure by x cm water column

A body is moving towards north with initial velocity of 13m/s. Its is subjected to a retardation of 2 m/s^{2} towards south.The distance travelled in 7th sec is ??

**Asked By: NIKHIL VARSHNEY**

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**Joshi sir comment**

displacement of any particular sec. = u+at-(a/2)

here direction of motion is opposite to the direction of acceleration so formula will be u-at+(a/2)

displacement in 7th sec = 0

now we know that direction of motion will become south after 6.5 sec. so distance for last half sec = ut+(1/2)at^{2 }= 1/4

same will be the distance for the first half sec of 7th. so total distance for 7th sec = 1/4 + 1/4 = 1/2