You won't need to worry about what's your final velocity what's your initial velocity you know you've got half into we know mass is 18 then v final is four you square and then this is half into 80 what is your v initial it's four squared okay very very much important ladies and gentlemen i'm giving you as a quick test and as a quick tax a task listen please punch all of these minus all of this and tell me what answer you get okay obviously i know this is half of 80 which is 40 multiplied by 4 squared it should be something like 16 then you know it's like it's like a 40 times 16 you subtract 40 times 16.
Ladies and gentlemen you can see both of these are the same
so this minus that will obviously be equals to zero okay i hope ladies and
gentlemen you are able to notice where i'm heading with this okay so that means
all of these can now be equated to zero okay why can all of this be equated to
zero it's because the speed is constant but if the speed wasn't constant ladies
and gentlemen then it means there you're going to substitute the final velocity
whatever that it is and then you're going to substitute the initial velocity
which is different value from the final velocity and you're going to get a
value which is not zero okay on the right side of the equation or on the right
side of the equal sign okay so ladies and gentlemen.
Now please do allow me to equate the whole of these to zero
because you've seen why it can be equated to zero so that means delta k is
equals to zero why is it equals to zero it's because the speed of four meters
per second is constant okay that's what makes it to be zero there okay ladies
and gentlemen also please do make sure that you fully understand the meaning of
delta and what a you know it does to the formula okay do not just say because
you can see it's a k then you just say it's half mv squared then you substitute
it there because you're going to have 80 times that 16 it gives you a number
there then you work it out with the whole of this and it leaves in the wrong
directions okay so now can we just quickly work out the the left side of the
equal sign.
We know the tension is nine 960 okay multiplied by we know
the distance is 20 meters okay then because of the angle ladies and gentlemen
very very much important this is the part that i want to explain okay remember
guys this is that free body diagram okay so the force as a result of the
tension it's in that upward direction okay let me just quickly explain this in
a red marking pen so that it doesn't confuse you ladies and gentlemen so what
i'm trying to explain is that a the tension is pulling this soldier in the
upward direction okay so that means a that means the angle is equals to zero
decrease because a you know a it's in the same direction in which the soldier
it's moving.
But when it comes to anything in the opposite direction it
becomes a different story ladies and gentlemen for example we know we've got
force of gravity in that opposite direction okay it's in the opposite direction
not in the opposite direction but at an angle because there are no sideways a
motion everything is happening vertically upwards okay very very much important
ladies and gentlemen so that means that angle is now 180 degrees 180 degrees
which angle the angle as a result of force of gravity okay so ladies and
gentlemen let me also try to explain it in a different way i hope it will then
make sense let's say you've got a car
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