# Determine the force in each member of the Pratt roof truss shown. State whether each member is in tension or compression.

Question-AnswerCategory: Engineering MechanicsDetermine the force in each member of the Pratt roof truss shown. State whether each member is in tension or compression.
S cornwell asked 1 year ago

Determine whether the block shown is in equilibrium and find the magnitude and direction of the friction force when θ = 40° and P = 400 N.

Step: 1

Draw the free body diagram of the body as follows:

Step: 2

Apply the force equilibrium condition about x-axis.

Substitute 400 N for P and for .
…… (1)
Apply the force equilibrium condition about y-axis.

Substitute 400 N for P and for .
…… (2)

Step: 3

Substitute  for N in the equation (1).

Substitute 47.98 N for F in the equation (2).

Step: 4

Calculate the maximum frictional force.

Here, is the coefficient of static friction.
Substitute 0.20 for .

Since, , the block is in equilibrium.
Therefore, the frictional force is .