A thin hollow sphere of mass m is completely filled with a liquid of mass m. When the sphere rolls with a velocity v, kinetic energy of the system is (neglect friction)

 

1.  mv²

 

2.  mv²

 

3.  mv²

 

4.  mv²

 

A non-conducting body floats in a liquid at 20 °C with of its volume immersed in the liquid. When liquid temperature is increased to 100 °C, of body’s volume is immersed in the liquid. Then the coefficient of real expansion of the liquid is (neglecting the expansion of container of the liquid)

 

1.  15.6×10^-4oC^-1

Two slabs A and B of different materials but of the same thickness are joined end to end to form a composite slab. The thermal conductivities of A and B are K₁ and K₂ respectively. A steady temperature difference of 12 °C is maintained across the composite slab. If K₁ = , the temperature difference across slabs A is

 

1.  4 °C

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

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)