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Question
A ring consisting of two parts ADB and ACB of same conductivity k carries an amount of heat H. The ADB part is now replaced with another metal keeping the temperatures T1 and T2 constant. The heat carried increases to 2H. What should be the conductivity of the new ADB part? Given 
- 2 k
- 3 k
The correct answer is:
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physics-
Two sheets of thickness d and 2 d and same area are touching each other on their face. Temperature TA, TB, TC shown are in geometric progression with common ratio r = 2. Then ratio of thermal conductivity of thinner and thicker sheet are
Two sheets of thickness d and 2 d and same area are touching each other on their face. Temperature TA, TB, TC shown are in geometric progression with common ratio r = 2. Then ratio of thermal conductivity of thinner and thicker sheet are
physics-General
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The spectral emissive power 
for a body at temperature T1 is plotted against the wavelength and area under the curve is found to be A. At a different temperature T2 the area is found to be 9A. Then 
=
The spectral emissive power for a body at temperature T1 is plotted against the wavelength and area under the curve is found to be A. At a different temperature T2 the area is found to be 9A. Then =
physics-General
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An open vessel is filled completely with oil which has same coefficient of volume expansion as that of the vessel. On heating both oil and vessel,
An open vessel is filled completely with oil which has same coefficient of volume expansion as that of the vessel. On heating both oil and vessel,
physics-General
physics-
Heat is conducted across a composite block of two slabs of thickness d and 2d. Their thermal conductivities are 2k and k respectively. All the heat entering the face AB leaves from the face CD. The temperature in °C of the junction EF of the two slabs is :
Heat is conducted across a composite block of two slabs of thickness d and 2d. Their thermal conductivities are 2k and k respectively. All the heat entering the face AB leaves from the face CD. The temperature in °C of the junction EF of the two slabs is :
physics-General
physics-
Heat is conducted across a composite block of two slabs of thickness d and 2d. Their thermal conductivities are 2k and k respectively. All the heat entering the face AB leaves from the face CD. The temperature in °C of the junction EF of the two slabs is :
Heat is conducted across a composite block of two slabs of thickness d and 2d. Their thermal conductivities are 2k and k respectively. All the heat entering the face AB leaves from the face CD. The temperature in °C of the junction EF of the two slabs is :
physics-General
physics-
Two stars bound together by gravity orbit each other because of their mutual attraction. Such a pair of stars is referred to as a binary star system. One type of binary system is that of a black hole and a companion star. The black hole is a star that has collapsed on itself and is so massive that not even light rays can escape its gravitational pull. Therefore, when describing the relative motion of a black hole and a companion star, the motion of the black hole can be assumed negligible compared to that of the companion. The orbit of the companion star is either elliptical with the black hole at one of the foci or circular with the black hole at the centre. The gravitational potential energy is given by U = – Gm M/r, where G is the universal gravitational constant, m is the mass of the companion star, M is the mass of the black hole, and r is the distance between the centre of the companion star and the centre of the black hole. Since the gravitational force is conservative, the companion star’s total mechanical energy is a constant of the motion. Because of the periodic nature of the orbit, there is a simple relation between the average kinetic energy 
of the companion star and its average potential energy < U>. In particular, 
Two special points along the orbit are singled out by astronomers. Perigee is the point at which the companion star is closest to the black hole, and apogee is the point at which it is furthest from the black hole.
Which of the following prevents the companion star from leaving its orbit and falling into the black hole?
Two stars bound together by gravity orbit each other because of their mutual attraction. Such a pair of stars is referred to as a binary star system. One type of binary system is that of a black hole and a companion star. The black hole is a star that has collapsed on itself and is so massive that not even light rays can escape its gravitational pull. Therefore, when describing the relative motion of a black hole and a companion star, the motion of the black hole can be assumed negligible compared to that of the companion. The orbit of the companion star is either elliptical with the black hole at one of the foci or circular with the black hole at the centre. The gravitational potential energy is given by U = – Gm M/r, where G is the universal gravitational constant, m is the mass of the companion star, M is the mass of the black hole, and r is the distance between the centre of the companion star and the centre of the black hole. Since the gravitational force is conservative, the companion star’s total mechanical energy is a constant of the motion. Because of the periodic nature of the orbit, there is a simple relation between the average kinetic energy of the companion star and its average potential energy < U>. In particular, Two special points along the orbit are singled out by astronomers. Perigee is the point at which the companion star is closest to the black hole, and apogee is the point at which it is furthest from the black hole.
Which of the following prevents the companion star from leaving its orbit and falling into the black hole?
physics-General
physics-
Figure shows the orbit of a planet P round the sun S. AB and CD are the minor and major axes of the ellipse.
If U is the potential energy and K kinetic energy then 
at
Figure shows the orbit of a planet P round the sun S. AB and CD are the minor and major axes of the ellipse.
If U is the potential energy and K kinetic energy then at
physics-General
physics-
Figure shows the orbit of a planet P round the sun S. AB and CD are the minor and major axes of the ellipse.
If t1 is the time taken by the planet to travel along ACB and t2 the time along BDA, then
Figure shows the orbit of a planet P round the sun S. AB and CD are the minor and major axes of the ellipse.
If t1 is the time taken by the planet to travel along ACB and t2 the time along BDA, then
physics-General
physics-
v-t graph of an object of mass 1 kg is shown
v-t graph of an object of mass 1 kg is shown
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Two identical balls A and B are released from the positions shown in figure. They collide elastically on horizontal portion MN. All surfaces are smooth. The ratio of heights attained by A and B after collision will be(Neglect energy loss at M & N)
Two identical balls A and B are released from the positions shown in figure. They collide elastically on horizontal portion MN. All surfaces are smooth. The ratio of heights attained by A and B after collision will be(Neglect energy loss at M & N)
physics-General
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A car travelling on a smooth road passes through a curved portion of the road in form of an arc of circle of radius 10 m. If the mass of car is 500 kg, the reaction on car at lowest point P where its speed is 20 m/s is
A car travelling on a smooth road passes through a curved portion of the road in form of an arc of circle of radius 10 m. If the mass of car is 500 kg, the reaction on car at lowest point P where its speed is 20 m/s is
physics-General
physics-
The block A is pushed towards the wall by a distance and released. The normal reaction by vertical wall on the block B v/s compression in spring is given by :
The block A is pushed towards the wall by a distance and released. The normal reaction by vertical wall on the block B v/s compression in spring is given by :
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physics-
In a conical pendulum, the bob is rotated with different angular velocities and tension in the string is calculated for different values of 
. Which of them is correct graph between T &
In a conical pendulum, the bob is rotated with different angular velocities and tension in the string is calculated for different values of . Which of them is correct graph between T &
physics-General
physics-
Tangential acceleration of a particle moving in a circle of radius 1 m varies with time t as (initial velocity of particle is zero). Time after which total acceleration of particle makes and angle of 30° with radial acceleration is
Tangential acceleration of a particle moving in a circle of radius 1 m varies with time t as (initial velocity of particle is zero). Time after which total acceleration of particle makes and angle of 30° with radial acceleration is
physics-General
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At a given instant, A is moving with velocity of 5m/s upwards What is velocity of B at that time :
At a given instant, A is moving with velocity of 5m/s upwards What is velocity of B at that time :
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