Topic: Engineering Mechanics
In the figure shown, the minimum ratio of mu1/mu2 so that the masses move together with the application of force F is (Assume block A has 5 kg on top of block B with 10 kg, pulling A with force F)
- A. 5
- B. 2
- C. 4
- D. 3
Answer: D. 3
Explanation: For the blocks to move together as a single unit, the friction force applied to the top block A by the applied force F must be sufficient to overcome the static friction between block B and the ground. The maximum friction force between block A (5 kg) and B is F_fA = mu1 * (5 * g). The friction force between block B (carrying A, total 15 kg) and the ground is F_fB = mu2 * (15 * g). Equating the two friction forces gives mu1 * 5 * g = mu2 * 15 * g. Solving for the ratio yields mu1 / mu2 = 15 / 5 = 3.