1.

Two blocks of masses m1 = 1 kg and m2 = 2 kg are connected by non-deformed light spring. They are lying on a rough horizontal surface. The coefficient of friction between the blocks and the surface is 0.4. What minimum constant force f has to be applied in horizontal direction to the block of mass m1 in order to shift the other block? (take g = 10 m/s2)

Answer»

My APPROACH was to set the force on m2 = 0, so the spring force equals the friction force. Then I set the force on M1 = 0, so the force equals the spring force plus the friction force on m1. This gives the answer as F=k(m1+m2)g.

However the correct solution is found by SETTING the WORK done by BLOCK 1 = 0, which gives k(m1+(m2)/2)g.



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