Calculating Tension in a Falling 5kg Brick on a Rope | Homework Problem

[demonslayer42]

Homework Statement

A 5kg brick on a rope is lowered towards the ground. While the brick is accelerating downward at 1.5m/s^2, find the tension in the rope. What is the reaction force to the upward force of tension acting on the brick?

Homework Equations

Sum of F = ma
w = Fg = mg
g = 9.8 m/s^2

The Attempt at a Solution

So basically what I did was drew a diagram.

/\ T
#
#
# a = -9,8 m/s^2
#
#
\/ W = mg = 5.0(9.8) = 49 N

T = mg + ma = 49 + 5.0(-1.5) = 41.5 N

O.k. where did i go wrong? lol I can't figure this out and it's driving me crazy

 

[PhanthomJay]

Doesn't look wrong to me...why do you think it is wrong?

 

[demonslayer42]

Because I always do something wrong...You sure it's correct? I'm just really shocked I got it correct it seems to easy i must be missing something.

 

[PhanthomJay]

You noted correctly that T=mg + ma, where a is negative. How did you arrive at that equation? That's the most important part.