Helicopter Lifting off(Newtons Laws). Help please?

[bob24]

Homework Statement

A medical helicopter weighs 7000 lbs. How much upward force must the propeller supply for it to lift off at 10ft/sec(squared)?

Homework Equations

T-w=ma, w=mg

The Attempt at a Solution

Here is what I tried:
T-w=ma.....w=mg---7000=m(32.2)=217.39k
T-7000= 217.39(-10ft/s)
T=4826.1

What am I doing wrong here? Shouldnt the acceleration be a negative value since it is going upward? and what should the actual final answer be?

 

[yeahhyeahyeah]

F = m * a

now, to go up, it must counter both gravitational acceleration, plus add that additional 10 ft/sec acceleration

so "a" = 10 ft/sec + ...

 

[bob24]

I see, thank you.
So technically, the only thing I did wrong was the negative sign.

 

[yeahhyeahyeah]

Yeah, because if you're doing T-w then you're saying that 'g' is acting in the negative direction since you're subtracting it from upward force. Since the 10 ft/s are in the opposite direction from g, it can't be negative TOO