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Two blocks A (1 kg) and B (2 kg) are con...


Two blocks A (1 kg) and B (2 kg) are connected by a string passing over a smooth pulley as shown in the figure. B rests on rough horizontal surface and A rest on B. The coefficient of friction between A and B is the same as that between B and the horizontal surface. The minimum horizontal force F required to move A to the left is 25 N. The coefficient of friction is:

A

0.67

B

0.5

C

0.4

D

0.25

Text Solution

Verified by Experts

The correct Answer is:
B
Let `f_1` be the magnitude of limiting frictional force between the blocks and `f_2` be the magnitude of limiting frictional forcfe between the blocks and horizontal surface. The free body diagrams for both the blocks is as shown . Applying Newton's second low to both the blocks
`F-f_1-T=m_Aa` (1)
`F-f_1-f_2=m_Ba` (2)
For F to just pull the blocks, acceleration of blocks `a=0`.
Therefore from equation (1) and (2) ,
`F=2f_1+f_2` or `25=mu(2xx1xx10+2xx10)` solving we get `mu=0.5`
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