3 ) The fog droplet falls vertically through air with acceleration equal to . . . . . . . . . . . : - A ) finite , B ) infinite , C ) zero ,

1 ) Can an instantaneous velocity of an object be equal to the average velocity of an object ?

When the acceleration is zero or velocity is constant .  So distance - time graph will be straight .

 

2 ) When a bullet is fired by a gun , the gun recoil backward with a velocity    . . . . . . . . . . that of bullet .

A ) greater than ,                                                                  B ) lesser than ,       

C ) equal to ,                                                             D ) None of these ,

Correct Answer : -   C ) equal to ,

 

3 ) The fog droplet falls vertically through air with acceleration equal to . . . . . . . . . . . : -

A ) finite ,                                                                   B ) infinite ,

C ) zero ,                                                                    D ) None of these ,

Correct Answer : -   C ) zero ,

Because fog droplet when falling vertically in air experience " air drag forces "

Air drag force = gravitational force " g " .

Fnet = 0 ,

So ma = 0 ,

So a = 0 .    And it means acceleration will be zero .

 

4 ) Static equilibrium : - When body is at rest .

Dynamic equilibrium : - When body is moving with uniform velocity .

 

5 ) The drift velocity of free electrons is of order of  10 ^ ( -5 )  m / s .

 

6 ) The ratio of numerical values of average velocity and average speed of a body is always . . . . . . . . . . . ,

A ) finite ,                                                                   B ) infinite ,

C ) unity or less ,                                                      D ) None of these ,

Correct Answer : -   C ) unity or less ,

 

7 ) At the top of trajectory of a projectile , the direction of its velocity and acceleration are . . . . . . . . . . . to each other .

A ) perpendicular ,                                                               B ) parallel ,

C ) None of these ,

Correct Answer : -   A ) perpendicular ,

 

8 ) A boat of mass 4o kg is at rest .  A dog of mass 4 kg moves in the boat with a velocity of 10 m / s . What is velocity of boat ?

A ) 1 m / s ,                                                                B ) 2 m / s ,

C ) 3.12 m / s ,                                                          D ) None of these ,

Correct Answer : -   A ) 1 m / s ,   

Solution : -

m1 v1 = m2 v2 ,

40 x v1 = 4 x 10 ,

v1 = 1 m / s , Answer .