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Question: Answered & Verified by Expert
A door $1.6 \mathrm{~m}$ wide requires a force of $1 \mathrm{~N}$ to be applied at the free end to open or close it. The force that is required at a point $0.4 \mathrm{~m}$ distance from the hinges for opening or closing the door is
PhysicsRotational MotionKCETKCET 2009
Options:
  • A $1.2 \mathrm{~N}$
  • B $3.6 \mathrm{~N}$
  • C $2.4 \mathrm{~N}$
  • D $4 \mathrm{~N}$
Solution:
1486 Upvotes Verified Answer
The correct answer is: $4 \mathrm{~N}$
Here, torque $\tau=1.6 \times 1=1.6 \mathrm{~N}-\mathrm{m}$ So, when $d=0.4 \mathrm{~m}$,
$\mathrm{F}=\frac{\tau}{\mathrm{d}}=\frac{1.6}{0.4}=4 \mathrm{~N}$

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