9can
u explain the 3 question clearly
A man climbs a flight of stairs. (Remember that he is not only moving forward but upwards as well.) Assume that he travels H height and L length(in horzontal distance)
Man's mass=M.
he carries a briefcase of mass m
Explain (or)and find the work done by each of these.
1) Gravity = ?
2) Normal Reaction = ?
3) Friction is << μmgS (explain)
4) briefcase
Want full explanations. Not as easy as most of you would think
A couple of answers are zero.. every one of you know.. But I think many many of you do not know why!
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18 Answers
62okie.. rohan i got u
But i am not very sure if u should have done that at the first place..
still good work :)
1and one thing u said that my explanation for the breifcase is wrong but i had written w.r.t briefcase
1i think it is because the legs dont slide over the surface the person lands his foot and then takes it up friction hence does negligible work
62no dear.. the answer would theoretically be zero... but practically i allowed compensation!!
93.
ok work by friction horizontally
=∫μmgcosθsinθdx vertically =∫μmgcos2θ
cos sin<1
resultant less than μmgl
62It is said that you need to prove that the work done by frictional force is not very large. ie. The work done by friction when a man moves the flight of stairs is negligible...
62the normal reaction explanation is correct
the briefcase is not correct!
Is the finger not moving in the ground frame!
1from the definition of work as long as normal reaction acts
the displacement of the point is 0
and the breifcase exerts the force on his fingers and w.r.t to the breifcase their is
no displacement of the finger (as it is moving along)
62ok.. atleast the explanations of part 2 and 4! (1 and 3 are relatively easy..)
62S = L (sorry)
Yeah and I want explanation for part 2, 3 part 4 (I think 1 u should have a different sign??)
1gravity = (M+m)gH
normal reaction =0
for the third part what is actually S
briefcase work done =0
9
1) (M+m)gH
2) 0 force perpendicular to disp
3)can be clear with question
4)0 disp 0