Answer:8.125 kg
Explanation:
Given
deceleration of elevator [tex]a=1.4\ m/s^2[/tex]
suppose T is the tension in the cord
therefore net force on lamp is
[tex]F_{net}=T-mg[/tex]
[tex]F_{net}=ma[/tex]
direction of a and g is in the same direction
[tex]T-mg=m(1.4)[/tex]
[tex]T=m(g+a)[/tex]
[tex]m=\dfrac{T}{g+a}[/tex]
[tex]m=\dfrac{91}{9.8+1.4}[/tex]
[tex]m=8.125\ kg[/tex]
