question_answer

The minimum force required to move a body of mass m vertically upward is

A)  a mg          

B)  \[mg/2\]

C)  more than 2mg

D)  more than mg

Correct Answer: D

Solution :

 Let us assume that body is moving upwards with acceleration a. The weight, \[w=mg\] of the body acts downward. At equilibrium, \[R=mg\] Now, when the body starts moving upward, then we have \[R-mg=ma\] \[\Rightarrow \] \[R=mg+ma\] This shows that an additional force (ma) is required to lift up the body. Hence, minimum force required is \[(mg+ma)>mg\]