A quiz qusetion

[cowgiljl]

The question is an 8.00 kg block (A) resting on a horizonal surface is attached to a 5.00kg block (B) that hangs freely by a string over a pulley. The coefficient of friction for block(A) is .200
a) calculate the acceleration of the system?
b) how long does it take the blocks to move 20 meters?

I drew a picture adn this is what i have using the formula for accel.
A = M2g-Mk*M1g/M1+M2 which gave me 5 (9.80)-.200*(8)*(9.80)/ 5+8 = 2.56 m/s^2

that was all i was able to get was i right so far and could help me on finding where i went wrong on this problem

[jamesrc]

What you did is correct (though you should be more careful with your parenthesis for the sake of those of us reading your post). To find the answer to part b, use your equations for constant acceleration motion. I would assume this system starts at rest, so s - so = vo*t + .5*a*t^2 would be the way to go, with vo = 0.