Q. A block of mass m is at rest under the action of force F against a wall as shown in figure. Which of the following statement is incorrect?

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A block of mass m is at rest under the action of force F against a wall as shown in figure. Which of the following statement is incorrect?

Solution:

This is the equilibrium of coplanar forces. Hence,

$hspace15mm boldsymbol{Sigma}f_x=0, , , therefore F=N$

$thereforehspace15mm boldsymbol{Sigma}_y=0,, , , , , , , , , , f=mg$

$hspace20mm boldsymbol{Sigma}tau=0 , , , , , , , tau_N+tau_f=0$

$therefore, , , , , Since, , , , , , , , tau_fne 0, , , , , therefore , , , , , tau_N ne 0$

$therefore, , , , .$Correct answer is (d)