You just choose the relevant formula okay so ladies and gentlemen let's now uh write our formula which is the work net remember they said use the work energy theorem. Okay so this is work this is energy combined is the wake energy theorem okay so that's why we equate energy I mean the work and the energy so this k ladies and gentlemen it's another type of energy which is kinetic energy it refers to a object moving at a particular speed okay we also have potential energy which are the objects which gain energy as they gain some height okay.
So ladies and gentlemen we've got wake net which is equals
to delta k okay so what is the work net ladies and gentlemen the wet net is the
work done by the tension plus the work as a result of gravity plus the work as
a result of friction and this is equals to delta k so what is delta k ladies
and gentlemen we know the formula for k is half mv squared so we already have
the formula for a k then what about this delta ladies and gentlemen delta is
changed that's where you say final minus initial of whatever that is the change
of or the change in so in this case we've got change in kinetic energy so that
means it will be delta of k.
So ladies and gentlemen that means we have kinetic energy
final minus kinetic energy initial okay very very much important ladies and
gentlemen what i'm actually doing now is just to formulate a you know using the
work energy theorem okay so i assume you fully understand ladies and gentlemen
so now a work as a result of that tension ladies and gentlemen so that means
we've got a tension remember tension is a force okay tension multiplied by
delta y okay before i continue with that ladies and gentlemen remember work is
equals to force times let me just say a distance and this is measured in joules
okay very very much important so that means this is a force in newton it should
be multiplied by a distance which should be in meters.
Okay so that's why here we've got a force multiplied by
delta y which is the distance multiplied by cos angle multiplied by cos angle
so ladies and gentlemen is this formula so now i'm just expanding each of these
a by that okay so that's why i'm saying a t which is first as a result of
tension it's that one ladies and gentlemen so even if you say force multiplied
by delta y cause that as long as you know that force is your tension otherwise
you can still say ft but otherwise you can just say t okay so now you add with
a the force of a you know the work as a result of fossil gravity so that means
this is the work as a result of tension this will be the work as a result of a
frictional force and no no a gravitational force but this is the work as a
result of frictional force and the whole of this is net because it's total
which is equated to k final minus k initial so now we are there ladies and
gentlemen we know mg is the force as a result of gravitational acceleration.
Okay so it becomes mg multiplied by delta y so remember guys
mg is just a force okay that's why we multiply this mg by delta y so it's more
like its force of gravity being multiplied by delta y then it makes it work as
a result of gravity as a result of gravity okay very very much important ladies
and gentlemen that you understand where these formulas are coming from because
one thing for sure i've realized most of learners they actually get confused by
these formulas not that they are not able to see what forces are acting on that
particular object okay then a we can now multiply by cause angle okay plus
ladies and gentlemen wag a as a result of friction which is equated to change
in k let me say change in k which is all of that i'm going to quickly explain a
a little bit more about change in k okay.
Ladies and gentlemen remember delta k a that means is half m
v squared a this will be v initial i mean v final then you subtract half m v
initial squared okay so that means ladies and gentlemen the whole of this it's
supposed to be equated to that but because i haven't got enough space there i'll
just say delta k and i will expand that delta k here because i want to explain
something remember ladies and gentlemen we know the mass is a 80 kg okay so can
we just substitute 80 kg there ladies and gentlemen let's say this is 80 at kg
okay 80 kg so now we just substituted the value for the mass you will
understand towards the end exactly what i'm trying to explain to you guys so
that means we now need the value of velocity and they said it's traveling at a
constant speed of four meters per second okay so guys this is where you need
this information of constant speed in capital letters what what does it mean or
how is it going to help you ladies and gentlemen.
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