A lamp hangs vertically from a cord in a descending elevator thatdecelerates at

Question

A lamp hangs vertically from a cord in a descending elevator thatdecelerates at 2.4 m/s2. (a) If the tension in the cordis 89 N, what is the lamp’s mass? (b) What is thecord’s tension when the elevator ascends with an upwardacceleration of 2.4 m/s2?
Iknow the answer, m=7.4kg and T=89N, but I don't understand why whenworking the problem the formula is T=m(g+a) both times, because isn't the acceleration (a) down the firsttime and up the second time? Wouldn't this makeit T=m(g+a) and T=m(g-a)
I'm not wording my question very well, but I need to know whyyou add 9.8 and 2.4 both times, instead ofsubtracting 9.8-2.4 the first time and adding 9.8+2.4 the second time.
Thanks!
Iknow the answer, m=7.4kg and T=89N, but I don't understand why whenworking the problem the formula is T=m(g+a) both times, because isn't the acceleration (a) down the firsttime and up the second time? Wouldn't this makeit T=m(g+a) and T=m(g-a)
I'm not wording my question very well, but I need to know whyyou add 9.8 and 2.4 both times, instead ofsubtracting 9.8-2.4 the first time and adding 9.8+2.4 the second time.
Thanks!

Explanation / Answer

I can work out the entire problem if you want. But here is a intuitive reasoning why you have to add "g" and "a"both sides - In both cases, the elevator is ACCELERATING UPWARDS IN PART A..THE ELEVATOR IS GOING DOWN.. BUT THE ACCELERATION ISSTILL 2.4m/s2 UPWARDS. Think what would happen if as u say, the acceleration is2.4m/s2 downwards. The elevator would gain speed due toacceleration. which not what is said. the elevator must slow downor decelerate. Either take acceleration to be 2.4 upwards OR UCAN TAKE IT TO BE - 2.4 DOWNWARDS PART B is obvious Hope I have answered ur question plz rate well

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