Answer
Mass of the lamp$=7.3$ $kg$
Work Step by Step
Let $m$ be the mass of the lamp and $T$ be the Tension in the cord.
Let the upward direction be $positive$ (sign convention)
Net force is given by:
$F_{net}=ma$
Writing the force equation using proper sign convention gives:
$F_{net}=T-mg$
$ma=T-mg$
Substituting the known values and solving gives:
$2.4m=89-9.8m$
$9.8m+2.4m=89$
$12.2m=89$
$m=\frac{89}{12.2} = 7.29$ $kg$
$m\approx 7.3$ $kg$
