# Maximum Tension

1. Sep 18, 2009

### Amel

1. The problem statement, all variables and given/known data

A 1.49 kg mass is suspended from a string which is pulled upward. The mass accelerates upwards with an acceleration of 3.10 m/s2. What is the tension in the string?

2. Relevant equations

Fnet= T + Fg =ma

so

T = m(a + g)

3. The attempt at a solution

Ok so I pluged in the numbers

T = (1.49kg)(3.1m/s2+(9.89m/s2)

and I got 19.221 kN but its wrong.

The title for this is wrong I was going to ask another question originally.

2. Sep 18, 2009

### CFDFEAGURU

3.1 m/s^2 is accelerating the mass upwards. Ask yourself, what direction is the 9.81 m/s^2 acting in? Draw a free body diagram of the forces acting on the mass.

Thanks
Matt

3. Sep 18, 2009

### Amel

I know gravity is downwards but there is a problem in the book just like this and this is how they get to that equation.

T + Fg = ma

so since Fg is negative

T - mg =ma

T = ma+mg

T = m(a+g)

I know that gravity was negative but thats why they added mg over to the other side.

4. Sep 18, 2009

### CFDFEAGURU

Yes, sorry I looked right past that. Not sure where you went wrong then. Are you close to the correct answer?

Thanks
Matt

5. Sep 18, 2009

### Amel

It just says 19.221 kN is wrong it doesen't tell me anything else. Are my units right? I don't get why im getting this wrong.

6. Sep 18, 2009

### CFDFEAGURU

The units are correct. N = kg*m/s^2.

Not sure why it isn't right. Maybe someone can help us both out. LOL

Thanks
Matt

7. Sep 18, 2009

### Amel

I was getting it wrong because I was putting kN instead of N. I missed that the book converted their answer to kN, Thanks I needed to see N = kg*m/s^2 to catch my mistake.

8. Sep 18, 2009

### CFDFEAGURU

LOL geeze I missed it too. Whoops.

Thanks
Matt