Answer
(a) (4) all of the preceding.
If the elevator is moving with an acceleration equal to g downwards, then
Measured weight$=m(g-g)=m\times0=0$
If the elevator is moving with acceleration in between 0 and $9.8\,m/s^{2}$ downwards, then
the measured weight will be in between 0 and 4900 N.
If the elevator is accelerating upwards, i.e., moving with some positive acceleration a, then
the measured weight will be m(g+a) which is more than 4900 N.
Therefore, the correct option is (4).
(b) Elevator accelerates downwards at 1.8 $m/s^{2}$.
Work Step by Step
(b) Measured weight= m(g+a)= 4000 N
$mg+ma=4000\,N$
$\implies 4900\,N+ma=4000\,N$
which gives
$500\,kg\times a=-900\,N$ Or
$a=\frac{-900\,N}{500\,kg}=-1.8\,m/s^{2}$
The negative sign shows that the acceleration is downwards.
