MHT CET 2019 :: Physics :: General questions

• Physics - General questions

The magnetic dipole moment of a short magnetic dipole at a distant point along the equator of the magnet has a magnitude of 'X' in SI units. If  the distance between the point and the magnet  is halved then the magnitude of the dipole moment will be 

Answer:

Explanation:

 The magnetic dipole moment is the product of either of pole strength and the magnetic length of dipole. Thus, it is independent of the distance of the point at which it is measured. So, it remains  unchanged, if the distance between point and the magnet is halved

An aircraft is moving with a uniform velocity of 150 m/s  in space. If all the forces acting on it are balanced, then it will 

Answer:

Explanation:

 As all the forces acting on the aircraft are balanced, so the net force on it will be zero, i.e,  no external force act on it. Thus, the aircraft will keep moving with the same velocity  of 150 m/s in the space

What is the minimum energy required to launch a  satellite of mass 'm' from the surface of the earth of mass 'M'  and radius  'R'  at an altitude 2R?

Answer:

Explanation:

 The minimum energy required to launch a satelite  from surface of earth  is equal to the amount of work done against gravity to move it from  the surface of earth  to a height h and is given by

$U=W=GMm(\frac{1}{r_{1}}-\frac{1}{r_{2}})$

  $=GMm(\frac{1}{R}-\frac{1}{R+h})$

 Here, h= 2R

$\Rightarrow $    $U=GMm(\frac{1}{R}-\frac{1}{3R})=\frac{2GMm}{3R}$

When  light entres glass from vacumm, then the wavelength  of light 

Answer:

Explanation:

 When light enters glass from the vacuum, then the wavelength of light decreases.

 This is because the speed of light in glass is less than that in the vacuum.

 From Snell's law, the refractive index in a medium  is given by  

             $\mu=\frac{c}{v}$

The glass is of higher refractive index than vacuum, so speed of light decreases and as the speed of light is directly proportional to the  wavelength  (c= v $\lambda$) , so the wavelength also be decreases.

 Two pendulums begin to swing simultaneously. The first pendulum makes nine full oscillations when the other makes seven. The ratio of the  lengths of the two pendulums is 

Answer:

Explanation:

 As two pendulums begin to swing  simultaneously , then

    n₁T₁   = n₂ T₂    ...........(i)

 where n₁  and n₂ are the numbers of oscillations of the first and second pendulum respectively and T₁ and T₂ be their respective time periods.

  The time period of simple  pendulum is given by

  $T=2\pi\sqrt{\frac{l}{g}}$

 where, l= length  of pendulum

and g= acceleration  due to gravity

  $\Rightarrow$    $  T^{2}\propto l$  .......(ii)

 So, from  Eqs. (i) and (ii), we get

     $\frac{l_{1}}{l_{2}}=\frac{T_1^2}{T_2^2}=\frac{n_2^2}{n_1^2}$

   Here, n₁=9, n₂=7

$\Rightarrow$   $\frac{l_{1}}{l_{2}}=\frac{(7)^2}{(9)^2}=\frac{49}{81}$

 Hence, the ratio of pendulum  lengths l₁:l₂= 49 :81

• Physics - General questions