# How to find mass in an Atwood machine

1. Oct 7, 2015

### iyanna

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

A pumpkin and a weight are attached to a frictionless pulley. As the 5kg weight is released, the pumpkin accelerates down at 4.65 m/s^2 to the ground. What is the mass of the pumpkin?

2. Relevant equations

How do I find the mass?
3. The attempt at a solution

T=m1g
ma=m2g-T
m=m2g-T/a
m=m2g-49/4.65
m=10.53-m2g
m-10.53=m2g
10.53+5=15.53
m2=1.57kg

2. Oct 7, 2015

### haruspex

It says the pumpkin accelerates downwards. Does that make it more or less than 5kg?

3. Oct 20, 2015

### iyanna

More

4. Oct 20, 2015

### haruspex

You don't make it clear, but I assume you are using m ( or m1) for the mass of the weight and m2 for the pumpkin.
If T is the tension in the rope, what are the forces acting on the pumpkin? What "F=ma" equation does that give you? Same questions for the weight.

5. Feb 14, 2016

### Kamisama

I think your formula is off.

Shouldn't it be m2 = (ma + T) / g ?

6. Feb 14, 2016

### haruspex

How is that different from
?