2. A woman prevents a 3kg brick from falling by pressing it against a vertical wall. The coefficient of friction

is 0.6

a What force must she use?

The downward force is the weight of the block which can be calculated by W = mg = 3*10 = 30 N

So the frictional force must be equal to 30 N to prevent the block from fall.

So to calculate the normal reaction (the force exerted by the women)

F = xR

Where F = frictional force

x = coefficient of friction

R = normal reaction.

By substituting you can get,

30 = 0.6 * R

R = 50 N

R=30 that's the answer