# Pully with 2 blocks friction question

1. Mar 19, 2012

### algar32

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

Two blocks are connected by a string that goes over an ideal pulley as shown in the figure and pulls on block A parallel to the surface of the plane. Block A has a mass of 3.00 kg and can slide along a rough plane inclined 30.0° to the horizontal. The coefficient of static friction between block A and the plane is 0.400. What mass should block B have in order to start block A sliding up the plane?

2. Relevant equations
http://ScrnSht.com/ftjykb
figure^^
3. The attempt at a solution
.4 x cos30 x 9.81 x 3kg = 10.2 =all forces down hill
ften = block b mass* 9.81
ftension must be equal to this to get the block started
10.2 = m x 9.81
m= 1kg

2. Mar 19, 2012

### tal444

This part is wrong. F$_{gravity}$ = mgsin30 and F$_{friction}$ = μmgcos30.

3. Mar 19, 2012

### emailanmol

As pointed out by Tal444,
Tension will not be equal to 10.2

Tension is acting against two forces.
Force of friction and force of gravity (component along plane )