Question

An eraser weighing $1\,N$ is pressed against a vertical black board with a normal force of $5\, N$. The coefficient of friction $\mu$ between eraser and Blackboard 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

Answer 1

Answer: (A)

2N

Answer 2

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,
$R=5N,\mu =0.4$
$\therefore$ $F=0.4\times 5=2\,N$