Question

when a boy weighing sits at one end of a 4m long see saw it gets depressed at its end.how can it be brought to the horizontal position by a man weighing 40kgf

Answer 1

if a boy is siting at one end of see saw its a lever, as to lift him consider him load so to balance out the lever with a 40 kg man,who is effort. we have to follow:
$effort \: arm \div load \: arm$
ie. if the boy is light the 40 kg man has to sit closer to the fulcrum .

to consider: the distance between load and fulcrum is load arm and the distance between the effort and fulcrum is effort arm

solved with lever mechanics