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 .
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