2 blocks, each on an inclined plane

1. Jan 18, 2010

RonakPat

1. The problem statement, all variables and given/known data
Two 2kg blocks are joined by a massless cord and pulley, ignoring friction, determine each block's acceleration using a free body diagram for each.

Picture for visual aid: http://img27.imageshack.us/img27/2653/86460048.png [Broken]

3. The attempt at a solution
I did the free body diagrams and solved for the tension on the string to try to equate the two sides

for the first block i got: T - mgsin30 = ma(1) so T = ma(1) + mgsin30
for the second block i got: mgsin60 - T = ma(2) so T = mgsin60 - ma(2)

The problem is the fact that i have two variables that i am solving for. I can't figure it out

Last edited by a moderator: May 4, 2017
2. Jan 18, 2010

tiny-tim

Welcome to PF!

Hi RonakPat! Welcome to PF!

You're missing the obvious …

the length of the string is constant, so a1 + a2 = 0.

(some people call that a geometric constraint)

3. Jan 18, 2010

RonakPat

Re: Welcome to PF!

So should I still set the two things equal then substitute one of the accelerations(a2) out to find the other(a1) then use what you gave me to find the other(a2)?

4. Jan 18, 2010

tiny-tim

Equal and opposite, yes.

5. Jan 18, 2010

RonakPat

Well i solved it and it came out to be 1.79m/s2. Does it matter which of them has the negative acceleration or do both have equal positive accelerations?

6. Jan 18, 2010

tiny-tim

hmm … well, you'd better say that one goes upward with acceleration 1.79m/s2, and the other goes downward …

you'll have to make it clear you know which way they're going!