Question

A block of mass $mkg$ is kept on a weighing machine in an elevator. If the elevator is retarding upward by an acceleration of $am/s^2$, the retarding reading of weighing machine is (in kgf) will be :

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

Answer 1

The correct option is B $m(g-a)$

retarding upwards means elevator has downward acceleration $\left(a\right)$ & block will experience pseudo force $ma$ upwards FBD of block

$N=m(g-a)$

Hence reading of weighting machine is $N=m(g-a)$