Tension and Normal Force in a Moving Elevator

[patelkey]

A 5.0 kg mass is suspended by a string from the ceiling of an elevator that
is moving upward with a speed which is decreasing at a constant rate of 2.0
m/s in each second. What is the tension in the string supporting the mass?

-I know that the Normal Force on the string is Fn=mg so it would be equal to 49 N, however how would I use the rest of the information to calculate the tension in the string. I know that the answer is supposed to be 39 N but I don't know how to approach it from this point.

 

[elliotr]

2.0 m/s/s means that there is an additional force caused by the deceleration of the elevator (negative acceleration), and F=ma. Therefore f_total = 49N - 5kg*(2m/s^2) = 39N

 

[patelkey]

okk that's what I was thinking but I felt as if it was just a guess that happened to work out thanks for the explanation