Question

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

• A. $0$
  
• B. $40$
  
• C. $20$
  
• D. $2$
  

Answer 1

Answer: (A)

$0$

Mass of the body $m=2kg$

Acceleration of lift in downward direction $a=g$

Let the reading of spring balance be $N$.

Equation of motion for the body : $ma=mg-N$

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

$⟹$ $N=mg-mg=0$

Thus the spring balance will show zero reading.