Laws of MotionHard
Question
Given mA= 30kg, mB = 10kg, mC = 20 kg . The coefficient of friction between A and B μ1 = 0.3, between B and C μ2 = 0.2 and C , ground, μ3 = 0.1. The least horizontal force F to start motion of any part of the system of three blocks resting upon one another as shown in figure is (g = 10 m/s2)
Options
A.60 N
B.90 N
C.80 N
D.150 N
Solution
Maximum value of f1 = 0.3 × 30 × 10 = 90 N
Maximum value of f2 = 0.2 × 40 × 10 = 80 N
Maximum value of f1 = 0.1 × 60 × 10 = 60 N
⇒ Least horizontal force F to start motion = 60N
Maximum value of f2 = 0.2 × 40 × 10 = 80 N
Maximum value of f1 = 0.1 × 60 × 10 = 60 N
⇒ Least horizontal force F to start motion = 60N
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