1 ) If the acceleration due to gravity at the earth’s surface is ( 9.8m/s2 ) and the mass of the earth is 80 times that of the moon and radius of earth 4 times that moon, the value of g at the moon’s surface will be ?
A ) 9.8m/s2 , B ) 1.96 m/s2 ,
C ) 4.9m/s2 , D ) None of these ,
Correct Answer : - B ) 1.96 m/s2 ,
Solution : -
Given Data : -
· ge = 9.8 m/s2 { ge = gravitational acceleration of earth } ,
· Me = 80 * Mm { Me = mass of earth , Mm = mass of moon } ,
· Re = 4 * Rm { Re = Radius of earth , Rm = Radius of moon } ,
· gm = ? ,
Formula : -
ge = GMe / (Re)^2 ,
So ,
Ø ge = G(80*Mm) / (4*Rm)^2
Ø ge = (80)GMm / (16)(Rm)^2
Ø ge = (5)GMm / (Rm)^2 ,
Ø ge = 5 * gm ,
Ø 9.8 = 5 * gm , (ge = 9.8 m/s2 )
Ø gm = 9.8 / 5 ( m / s2 ) ,
Ø gm = 1.96 m / s2 , Answer .
2 ) Centre of gravity is a point , where the whole ……………….. of body is to be centered .
A ) mass , B ) weight ,
C ) Both of these , D ) None of these ,
Correct Answer : - B ) weight ,
3 ) Find the velocity of pendulum in SHM which has amplitude of 0.2 m and time period of 0.01 sec ?
A ) 20 π , B ) 30 π ,
C ) 40 π , D ) None of these ,
Correct Answer ; - C ) 40 π ,
Solution : -
Given Data : -
· T = 0.01 s ,
· Xo = 0.2 m ,
· v = ?
Formula : -
v = r w .
So first we have to find value of omega ( w ) , so
Ø w = 2 π / T ,
Ø w = 2 π / (0.01) ,
Ø w = 200 π .
So We simply put it formula : -
Ø v = rw ,
Ø v = Xo * w ,
Ø v = ( 0.2 ) * ( 200 π ) ,
Ø v = 40 π . Answer
5 ) Centre of mass is a point , where the whole …………… of body is to be centered .
A ) mass , B ) weight ,
C ) Both of these , D ) None of these ,
Correct Answer : - A ) mass ,
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