Question

A block of mass $mkg$ is kept on a weighing machine in an elevator. If the elevator is retarding upward by $am{s}^{-2}$ the reading of weighing machine is (in $kgf$):

• A. $mg$
• B. $m(g-a)$
• C. $m\left(1-\frac{a}{g}\right)$
• D. $m(g+a)$

Answer 1

The correct option is D $m(g+a)$

Motion in an elevator or lift :

1) If the man inside the lift falls freely under gravity without any upward force then the apparent weight is zero.

2) If he falls with an acceleration a less than g then he experiences an upward force of m(g - a) and hence his apparent weight is m(g-a).

3) If he moves up with an acceleration a he experiences an upward force of m(g +a) and his apparent weight is equal to m(g + a).

From the explanations above the answer is :m(g+a)