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Question Number 210809 by mr W last updated on 19/Aug/24

Commented by mr W last updated on 19/Aug/24

$c a n t h e b o y l i f t h i m s e l f ?$
Commented by Ghisom last updated on 19/Aug/24

$if we use a machine coiling the rope instead$ $of a boy pulling it, it will work . there$ $should be no difference .$
Commented by mr W last updated on 19/Aug/24

$y e s . i a g r e e w i t h y o u . i f a h a n d w i n c h$ $i s m o u n t e d o n t h e b o x, p e o p l e m a y$ $s a g t h a t t h e b o y c a n l i f t h i m s e l f .$ ${i t}^{'} s a p o p u l a r t y p e o f l i f t w h i c h y o u$ $m a y s e e i n m a n y c o n s t r u c t i o n s i t e s .$ $i t i s t h e s a m e w h e n t h e b o y p u l l s$ $t h e r o p e .$
Commented by mr W last updated on 19/Aug/24

	Answered by mr W last updated on 19/Aug/24

	Commented by mr W last updated on 19/Aug/24

	$s a y t h e m a s s o f t h e b o y i s m_{1} = 50 k g,$ $t h e m a s s o f t h e b o x i n c l u d i n g t h e$ $p u l l e y s e t i s m_{2} = 20 k g .$ ${l e t}^{'} s s a y t h e b o x r e s t s o n a s c a l e .$ $w h e n t h e b o y {d o e s n}^{'} t p u l l t h e r o p e,$ $t h e s c a l e s h o w s j u s t t h e t o t a l w e i g h t$ $o f a l l t h i n g s, i . e . 70 k g (o r 700 N) .$ $n o w t h e b o y p u l l s t h e r o p e w i t h a$ $f o r c e T . a s s h o w n a b o v e,$ $N_{1} = T + m_{1} g$ $2 T + N_{2} = N_{1} + m_{2} g = T + m_{1} g + m_{2} g$ $\Rightarrow N_{2} = (m_{1} + m_{2}) g - T$ $w e s e e, t h e m o r e t h e b o y p u l l s t h e r o p e,$ $t h e l e s s t h e s c a l e s h o w s . w h e n t h e$ $b o y p u l l s w i t h a f o r c e (m_{1} + m_{2}) g,$ $t h e b o x w i l l l o s e c o n t a c t w i t h t h e$ $s c a l e . n o w w h e n h e g i v e s a l i t t l e$ $m o r e f o r c e, t h e y w i l l b e g i n t o m o v e$ $u p w a r d s .$ $t h e r e f o r e t h e b o y c a n l i f t h i m s e l f!$
	Commented by BHOOPENDRA last updated on 19/Aug/24

	$Y o u a r e r i g h t M r . W s i r A p p r e c i a t e T h a n k y o u$
	Commented by mr W last updated on 19/Aug/24

	$t h a n k s f o r y o u r c o n t r i b u t i o n t o o!$
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