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Plutonium decays within half-life of 24000 years. If the plutonium is stored for 72000 years, then the fraction of plutonium that remains is
A photon of energy 4 eV is incident on a metal surface whose work function is 2 eV. Minimum value of reverse potential to be applied for stopping the emission of electrons is
Velocity ratio of the two cathode rays is 1:2. They are applied to the same electric field. What is the deflection ratio of the two cathode rays ?
In an L-R circuit, time constant is that time in which current grows from zero to the value
A capacitor of capacitance 1 μ F is charged to 1KV. The energy stored in the capacitor in joules is
C = 1μF
V = 1KV
energy stored U = 1/2 (CV2)
= 1/2* 1*12 = 0.5
A sheet of aluminium foil of negligible thickness is introduced between the plates of a capacitor. The capacitance of the capacitor
A uniform chain of length L changes partly from a table which is kept in equilibrium by friction. The maximum length that can Withstand without slipping is l, then coefficient of friction between the table and the chain is
If R is the radius of a planet, g is the acceleration due to gravity, then the mean density of the planet is given by
A body cools from 60oC to 50oC in 10 min. If the room temperature is 25oC and assuming Newton's law of cooling holds good, then temperature of the body after the next 10 min will be
The kinetic energy of translation of 20 gm of oxygen at 47oC is (molecular wt. of oxygen is 32 gm/mol and R = 8.3 J/mol/K)
To convert a galvanometer into a voltmeter, we must connect a
To shield an instrument from external magnetic field, it is placed inside a cabin made of
If an object of weight W and density ρ is submerged in a fluid of density ρ₁, then apparent weight of the object will be
Which of the following affets the elasticity of a substance?
A car moves along a straight line whose motion is given by : s= 12t+ 3t2 − 2t2, where (s) is in metres and (t) is in seconds. The velocity of the car at start will be
The parametric equations of a curve traced by a projectile on a certain planet with no surrounding are given by :y = (8t-5t2) metre and x = 6t metre, where t is in seconds. The velocity with which the projectile is projected, is
Consider an elevator moving downwards with an accerleration a, the force exerted by a passenger of mass m on the floor of elevator is
When the displacement is half of the amplitude, then what fraction of the total energy of a simple harmonic oscillator is kinetic ?
A coin is placed on a horizontal platform, which undergoes vertical simple harmonic motion of angular frequency ω. The amplitude of oscillations is gradually increased. The coin will have contact with the platform for the first time. (i) at the higher position of the platform (ii) at the mean position of the patform (iii) for an amplitude of g/ω2 (iv) for an amplitude of √2/ω
A ray of light is incident on the hypotenuse of a right-angled prism after travelling parallel to the base inside the prism. If ' μ ' is the refractive index of the material of the prism, the maximum value of the base angle for which light is totally reflected from the hypotenuse is
A wheel rotates with a constant acceleration of 2.0 radian/sec2. If the wheel starts from rest the number of revolutions it makes in the first ten seconds will be approximately
The least coefficient of friction for an inclined plane inclined at angle α with horizontal in order that a solid cylinder will roll down it without slipping is
Correct Answer :- C
Explanation : Acceleration of point A must be zero due to pure rolling.
Thus mgsinα − f = 0 for point A
mgsinα − μmg cosα = 0
⟹ μ = tanα
50 g of copper is heated to increase its temprature by 10oC. If the same quantity of heat is given to 10 g water, the rise in its temperature is (Specific heat of copper = 420 Joule -kg-1oC-1. Specific heat of water = 4200 Joule -kg-1oC-1
What is the temperature of source in Carnot engine of 20% efficiency when heat exhausts at 27oC?
A stone is tied up to the end of a string and whirled in a vertical circle. The tension in the string is T1 when the stone is at the highest point and T2 when it is at the lowest point. Then
From following pairs, choose the pair that does not have identical dimensions
In Young's experiment of double slit, the intensity of central bright band is ---- times the individual intensities of the interfering waves
The number of beats produced per second by the vibrations x₁ = a sin 320 π t and x₂ = a sin 326 π t is
If the two slits in Young's experiment have width ratio 1:4, the ratio of intensity at maxima and minima in the interference pattern in
What will be the wave velocity, if the radar gives 54 waves per min and wavelength of the given wave is 10 m?
A bomb of mass 9 kg explodes into 2 pieces of mass 3 kg and 6 kg. The velocity of mass 3 kg is 1-6 m/s, the K.E. of mass 6 kg is
4 m3 of water is to be pumped to a height of 20 m and forced into a reservoir at a pressure of 2*105 N/m2 . The work done by the motor is (external pressure = 105 N/m2)
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