Question

A spring balance attached to the roof of a moving elevator indicates $80\text{kg}$ weight as the weight of a $120\text{kg}$ body. What is the acceleration of the elevation? (Take $g=10m/s^2$)

• A. $9.8{\text{m/s}}^2$
• B. $4.9{\text{m/s}}^2$
• C. $2{\text{m/s}}^2$
• D. $3.3{\text{m/s}}^2$

Answer 1

The correct option is D $3.3{\text{m/s}}^2$

Given measured mass = $80\text{kg}$
Actual mass = $120\text{kg}$
measured weight < Actual weight.
So lift must be moving down with acceleration and $N=m(g-a)$
meausured mass $m^{\prime }=\frac{N}{g}=\frac{m(g-a)}{g}$
$80=120\frac{(g-a)}{g}$
$a=g/3=10/3=3.33m/s^2$