question_answer

A block of mass m is at rest with respect to a rough incline kept in elevator moving up With acceleration a. Which of following statements is correct?

A) The contact force between block and incline is parallel to the incline.

B) The contact force between block and incline is of the magnitude \[m(g+a)\].

C) The contact force between block and incline is perpendicular to the incline.

D) The contact force is of the magnitude \[mg\,cos\,\theta \]

Correct Answer: B

Solution :

[b] in the figure, \[{{F}_{c}}=\sqrt{{{f}^{2}}+{{N}^{2}}}=m(g+a)\] \[f=m(g+a)sin\theta ,N=m(g+a)cos\theta \] Net contact force: \[{{F}_{C}}=\sqrt{{{f}^{2}}+{{N}^{2}}}=m(g+a)\]