Man in the lift

Classical Mechanics Level 4

A man of mass 60Kg standing on a light weighing machine kept in a box of mass 30Kg. The box is hanging from a pulley fixed to the ceiling through a light rope, the other end of which is held by the man himself. If the man manages to keep the box at rest, what is the weight(in Kg) shown by the machine ?

The answer is 15.

1 solution

Aquib Immanuel
May 19, 2015

For the man 60g=T+N...........(i) For the box 30g+N=T...........(ii) , (i)-(ii) --> 30g=2N --> N=15g
thus reading on scale is 15Kg
here T=tension N= normal contact force. g=acceleration of gravity

I think you should clarify the principles of your work.

$\sum { \overrightarrow { F } } =\overrightarrow { 0 } \Longrightarrow 60\overrightarrow { { { a }_{ 1 } } } +30\overrightarrow { { a }_{ 2 } } =\overrightarrow { 0 }$ that yields $\Longrightarrow 60\overline { { a }_{ 1 } } =-30\overline { { a }_{ 2 } }$ we also know that

$\\60{ a }_{ 1 }=60g-T \\ 30{ a }_{ 2 }=T -30g$

$T$ is the tension force. then $-2T=-30g\Longrightarrow\\T =15g\Longleftrightarrow { M }_{ shaun }=15Kg$

jafar badour - 6 years ago

Man in the lift

The answer is 15.

1 solution

0 pending reports