A mountaineer shouts his name in valley . Half a sec later , he hears the echo . How far away is the rock which is reflecting his voice ?

 1 )  A mountaineer shouts his name in valley . Half a sec later , he hears the echo . How far away is the rock which is reflecting his voice ?

A ) 80  m  ,                                               B ) 86  m  ,

C ) 82  m  ,                                              D ) None of these ,

Correct Answer : -  B ) 86  m  ,

Solution : -                                 

Given data : -

·          t = 0.5/2 sec = 0.25 sec        ( we divide time by 2 because voice took    0.5 sec ( half sec )  for both going towards rock and reflecting back to person .  And we just have to find distance between rock and person  in single direction ) ,

·          Speed of sound in air = 343 m/s ,

·          Distance = ?  ( between rock and person ) .

Formula : -

v = d / t ,

Ø    d = v x t   ,

Ø    d = 343 x 0.25

Ø    d = 85.75  m  ,  Answer .

 

2 ) A wire is bent into a ring of radius R and given a charge q .  The magnitude of electric field at the center of ring is ……. ,

A ) Infinite ,                                              B ) finite ,

C ) zero ,                                          D ) None of these ,

Correct Answer : -  C ) zero ,

 

3 ) The electric field due to an infinity long thin wire at a distance R varies as ……….. ( 1/R ) .

 

4 )  A particle is displaced from a position  2i - j + k to another position 3i - 2j +2k  under action of a force ( F = 2i - j + k ) . The work done by force is ?

A ) 2J ,                                             B ) 4J ,

C ) 8J ,                                             D ) None of these ,

Correct Answer : -  B ) 4J ,

Solution : -

Given data : -

F = 2i - j + k ,

d1 = 2i - j + k ,

d2 = 3i - 2j +2k ,

W = ?

Formula : -

W = F.d ,

d = d1 - d2 = ( 3 - 2 )i + ( -2 - (-1))j + ( 2 - 1 )k   =   1i - 1j +1k ,

So ,

W = (2)(1) + (-1)(-1) + (1)(1) ,

W = 4J  , Answer .

 

Now go to online quiz section and Physics Quiz 5 is uploaded related to these mcqs  , so check your preparation by this link : -

UG Online quizzes

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