# Newtons laws question.

1. Mar 18, 2010

### Dolly

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

Block A in the figure weighs 65.9N. The coefficient of static friction between the block and the surface on which it rests is 0.27. The weight w is 12.2N and the system is in equilibrium.

block A is placed on a table, it is connected by a string to a wall block w is hung off that string to form a 90degree angle between A and w and a 45degree angle between w and the wall.

A) Find the friction force exerted on block A.

2. Relevant equations

Fr = u Fn
F = ma

3. The attempt at a solution

i tried to find the net force using f = ma but there is no horizonal acceleration... so i am confused. :S help??

2. Mar 18, 2010

### drew212

There is no horizontal acceleration, but there is an acceleration due to gravity on block W.

First you need to calculate the static force of friction on block A:
F=UsFn
F=(0.27*65.9)
F=17.793

Then you need to determine if the tension on the string from block W has enough force to move block A:
F(b)=MA
F(b)=12.2(9.8)
F(b)=119.56

Therefore your answer is 18, keeping significant figures in mind.