question_answer

An eraser weighing\[1N\]is pressed against a vertical black board with a normal force of 5 N. The coefficient of friction\[\mu \]between eraser and Haclchoard is approximately 0.4. The force along the blackboard required to move the eraser is

A)  \[2N\]

B)  \[0.4N\]

C)  \[2.4N\]

D)  \[9.8N\]

Correct Answer: A

Solution :

 The eraser is pressed against the black board. Taking the vertical and horizontal components of forces, we have \[F=\mu R\] where, R is reaction of the board on the rubber. Given,        \[R=5N,\mu =0.4\] \[\therefore \] \[F=0.4\times 5=2N\]