First slide
Friction on horizontal surface
Question

In the figure given, the system is in equilibrium. What is the maximum value that W can have if the friction force on the 40 N block cannot exceed 12.0 N
 

Moderate
Solution

The free-body diagram of the block is as shown in adjacent figure.
 

f0max=12.0N( Given )T1max=12.0N
The free-body diagram of knot is as shown in adjacent figure.
 

T2sin30=W  (i) T2cos30=T1  (ii) 
Divide (i) by (ii), we get, tan30=WT1
or  W=T1tan30=0.577T1
Wmax =0.577T1max =0.577×12.0N=6.92N

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