Question

In the figure, two blocks are separated by a uniform strut attached to each block with frictionless pins. Block A weighs 400 N, block B weighs 300 N, and the strut AB weighs 200 N. If μ = 0.25 under block B, determine the minimum coefficient of friction under A to prevent motion. 

• A. \(0.4\)
• B. \(0.2\)
• C. \(0.8\)
• D. 0.1

Hint:

For struts or links hinged at both ends:
• Treat them as two-force members. 
• Forces always act along the axis of the member. 
• Check equilibrium of each block separately.

Answer 1

The Correct Option is A

Step 1: Since the strut is uniform and hinged at both ends, it is a two-force member. Hence, the forces at A and B act along the strut.
Step 2: Consider block B. The maximum friction force under B is fB = muB NB = 0.25 × 300 = 75 N
Step 3: Resolving forces along the strut direction, the force transmitted through the strut must be balanced by friction at B. This same force acts on block A.
Step 4: For block A, normal reaction is NA = 400 N Required coefficient of friction under A is muA = (fA)/(NA) = (160)/(400) = 0.4