Q143 / 150 · MHT CET 2022 (10 Aug Shift 2) · Physics

A door 1.2 mwide requires a force of $1 \mathrm{~N}$ to be applied perpendicular at the free end to open or close it. The perpendicular force required at a point 0.2 mdistant from the hinges for opening or closing the door is

  • A
    $2.4 \mathrm{~N}$
  • B
    $3.6 \mathrm{~N}$
  • Correct answer
    C
    $6.0 \mathrm{~N}$
  • D
    $1.2 \mathrm{~N}$

Solution

$\tau$ torque required to open/close the door will remain constant. $\begin{aligned} & \tau=r_1 \times F_1=r_2 \times F_2 \\ & 1.2 \times 1=0.2 \times F_2 \\ & \Rightarrow F_2=6 \mathrm{~N}\end{aligned}$

Hence, the correct answer is option: 'C'.

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