Question
Fri September 27, 2013 By: Rohan Astik

A lamp hangs vertically from a cord in elevator which is descending with an downward acceleration of a=2m/s2.the tension in the cord T=10.0N . what is the mass m of the lamp?

Expert Reply
Romal Bhansali
Sat September 28, 2013
The elevator is descending downwards with an acceleration a. The weight of lamp is also in the downward direction. The tension T acts in the vertical direction on the thread with which lamp is hung.
 
Thus, the balance equation of forces on the lamp is:
 
mg - T = ma
mg - ma = T
m(g - a) = T
Thus, m = T/(g - a) = 10/7.8 = 1.28 kg
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