Question

A door of $1.6\, m$ wide requires a force of $1 \,N$ to be applied at the free end to open or close it. The force that is required at a point $0.4\, m$ distant from the hinges for opening or closing the door is

• A. 3.6 N
• B. 2.4 N
• C. 4 N
• D. 1.2 N

Answer 1

Answer: (C)

4 N

Answer 2

Here, torque $\tau=1.6 \times 1=1.6\, N - m$
So, when $d=0.4\, m$,
$F=\frac{\tau}{d}=\frac{1.6}{0.4}=4 \,N$