# What is the mass of block on the left?

1. Sep 29, 2007

### aligass2004

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

The 100kg block in the figure below takes 6.6s to reach the floor after being released from rest. What is the mass of block on the left?

http://i241.photobucket.com/albums/ff4/alg5045/p8-33.gif

2. Relevant equations

F=ma
kinematic equation

3. The attempt at a solution

I tried using accleeration = velocity/time, and I got .023 m/s^2. Then I used velocity = displacement/time, and I got .152 m/s. And then I got completely lost.

2. Sep 29, 2007

### rootX

You should be using
d = 0.5at^2 (assuming that initial v is 0)

so get a, and then
you know the system is moving with a

therefore weight of larger mass - wieght of smaller mass = (total mass)*a

3. Sep 29, 2007

### aligass2004

Ok, for the acceleration I got .046m/s^2. How do I figure out what the total mass is since I don't know the smaller mass?

4. Sep 29, 2007

### learningphysics

you want to solve for the smaller mass... write the total mass in terms of the smaller mass...

5. Sep 29, 2007

### aligass2004

So larger mass-smaller mass = (larger mass + smaller mass)a

6. Sep 29, 2007

### learningphysics

(larger mass)*g - (smaller mass)*g = (larger mass + smaller mass)a

7. Sep 29, 2007

### aligass2004

Got it after three tries at manipulating the equation. 99.067kg.