In short wave communication, waves of which of following frequencies will be reflected back by the ionospheric layer having electron density 10¹¹ per m³?

 

1.  2 MHz

 

2.  10 MHz

 

3.  12 MHz

 

4.  18 MHz

A body of mass 4 kg moving with velocity 12 m/s collides with another body of mass 6 kg at rest. If two bodies stick together after collision, then the loss of kinetic energy of system is

 

1.  zero

A marble block of mass 2 kg lying on ice when given a velocity of 6 m/s is stopped by friction in 10 s. Then the coefficient of friction is

 

1.  0.01

 

2.  0.02

 

3.  0.03

 

4.  0.06

A body of mass 0.25 kg is projected with muzzle velocity 100 m/s from a tank of mass 100 kg. What is the recoil velocity of the tank?

 

1.  5 m/s

 

2.  25 m/s

 

3.  0.5 m/s

 

4.  0.25 m/s

A rocket with a lift off mass 3.5×10⁴ kg is blast upward with an initial acceleration of 10 m/s². Then, the initial thrust of the blasts is

 

1.  1.75×10⁵ N

A step-down transformer is used on a 1000 V line to deliver 20 A at 120 V at the secondary coil. If the efficiency of the transformer is 80%, the current drawn from the line is

 

1.  3 A

 

2.  30 A

 

3.  0.3 A

 

4.  2.4 A

What kV potential is to be applied on X-ray tube so that minimum wavelength of emitted X-rays may be 1 Å (h = 6.6×10^-34 J-s)

 

Hydrogen atom excites energy level from fundamental state to n =3. Number of spectrum lines according to Bohr is

 

1.  4

 

2.  3

 

3.  1

 

4.  2

A black body at a temperature of 2600 K has the wavelength corresponding to maximum emission 1200Å. Assuming the moon to be perfectly black body the temperature of the moon, if the wavelength corresponding to maximum emission if 5000 Å is

 

The heat required to increase the temperature of 4 moles of a monoatomic ideal gas from 273 K to 473 K at constant volume is