Question

A body of mass $2kg$ is hung on a spring balance mounted vertically in a lift. If the lift ascends with an acceleration equal to the acceleration due to gravity $g$, the reading on the spring balance will be (in $N$) :

• A. $4$
  
• B. $2$
  
• C. $20$
  
• D. $40$
  

Answer 1

Answer: (D)

$40$

Mass of the body $m=2kg$

Acceleration of lift in upward direction $a=g$

Let the reading of spring balance be $N^{\prime }$.

Equation of motion for the body : $ma=N^{\prime }-mg$

Or $mg=N-mg$ $(\because a=g)$

$⟹$ $N^{\prime }=2mg$

Thus reading of spring balance (in N) $N^{\prime }=2\times 2\times 10$

$\therefore$ $N^{\prime }=40N$