Kinematics - M1Watch

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Thread starter 14 years ago
#1
The book doesnt really tell you what exactly the following formulae is used for - only how to derive it:

v^2 = u^2 + 2as

Can someone please enlighten me

TIA
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14 years ago
#2
Its one of the equations of motion.

There are 4 i think:
v^2=u^2 + 2as
s=ut +(1/2)at^2
s=(1/2)(u+v)t
v=u+at

v is final velocity
u is initial velocity
s is displacment (distance from start)
a is acceleration (UNIFORM)
t is the time

They are used in M1 and M2 for basic acceleration questions and projectile questions.
Note. Projectiles have 2 components up or down / left or right.
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Thread starter 14 years ago
#3
(Original post by Syncman)
Its one of the equations of motion.

There are 4 i think:
v^2=u^2 + 2as
s=ut +(1/2)at^2
s=(1/2)(u+v)t
v=u+at

v is final velocity
u is initial velocity
s is displacment (distance from start)
a is acceleration (UNIFORM)
t is the time

They are used in M1 and M2 for basic acceleration questions and projectile questions.
Note. Projectiles have 2 components up or down / left or right.
Hey Syncman thanks for your reply. Thankfully I am understanding Kinematics much more better then Vectors.

I know you can use the formula v=u+at and then rearrange that to find just about anything, from velocity to initial velocity , to acceleration to time - except of course the displacement which is found via s=ut+1/2at^2. I am just a bit confused because if you can use v=u+at to find all what I have mentioned then what is the point of v^2=u^2 + 2as...

Thank you v much for helping me get to grips with mechanics! Its all v interesting btw.

P.S.

Will the formula booklets in the exam have any of the formulas for MEchanics listed in there?

Thanks again!
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14 years ago
#4
Nope... from what i remember. None of the linear acceleration equations are in the F/B.

There are 4 different formular because u may not have all of the information u need.
When i do an uniform acc Q. I ALWAYS write
s=
u=
v=
a=
t=

then read the question and fill them in. Look whats missing, and see what i have to find.

E.g.

A car passes A at 10ms^(-1) and accelerates at a constant rate of 5ms^(-2). It passes the finish line B which is 1km from A. How fast was the car going when it crossed the finish line.
s= 1000
u= 10
v = ?
a = 5
t = / (not required)
v^2 = u^2 + 2 a s
v = sqrt(10^2 + 2 * 5 * 1000)

This is jus one off top of my head so i aint gonna work it out lol
Hope this helps.
0
Thread starter 14 years ago
#5
(Original post by Syncman)
Nope... from what i remember. None of the linear acceleration equations are in the F/B.

There are 4 different formular because u may not have all of the information u need.
When i do an uniform acc Q. I ALWAYS write
s=
u=
v=
a=
t=

then read the question and fill them in. Look whats missing, and see what i have to find.

E.g.

A car passes A at 10ms^(-1) and accelerates at a constant rate of 5ms^(-2). It passes the finish line B which is 1km from A. How fast was the car going when it crossed the finish line.
s= 1000
u= 10
v = ?
a = 5
t = / (not required)
v^2 = u^2 + 2 a s
v = sqrt(10^2 + 2 * 5 * 1000)

This is jus one off top of my head so i aint gonna work it out lol
Hope this helps.
Thanks for the tip:

s=
u=
v=
a=
t=

I will remember that.

In the M1 book , page 40 example 3 they used the above formula for retardation, so I am wondering if it is only specifically for that.

Oh yes, do the earlier chapters get easier as you go through the later chapters?
0
14 years ago
#6
All the equations can be used for retardation.
Just put a = (-)5ms^(-2) (negative acceleration)

Yeah its the same with everything, the more u do the easier it is to do.
The uniform acceleration questions will be v.easy once uve done the chapter.

Just basically remember suvat and the formula for them and ur sorted basically.
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Thread starter 14 years ago
#7
(Original post by Syncman)
All the equations can be used for retardation.
Just put a = (-)5ms^(-2) (negative acceleration)

Yeah its the same with everything, the more u do the easier it is to do.
The uniform acceleration questions will be v.easy once uve done the chapter.

Just basically remember suvat and the formula for them and ur sorted basically.
What is the hardest chapter...warn me now!!!! so I am prepared! Surely there cant be anything as bad as Vectors in this whole book.
0
14 years ago
#8
(Original post by DOJO)
What is the hardest chapter...warn me now!!!! so I am prepared! Surely there cant be anything as bad as Vectors in this whole book.
Nope i think the last bit, force questions, inextensible strings.
2 body's connected by an inextensible string. one hanging off the table. when its dropped blah blah 0
14 years ago
#9
It is useful to have all 5 formulae as you will notice that each one omits one variable.

The derivations are straight forward:
Begin with v = u + at
Consider a v-t graph consisting of a constant acceleration (straight diagonal line) from, say, 0 to 20ms^-1.
You can appreciate that dist. = area under line
--> s = 1/2(v + u)t
Now: t = 2s/(v + u) = (v - u)/a
So: 2as = v^2 - u^2
And: v = u + at = 2s/t - u
So: s = ut + (1/2)at^2
And: u = v - at = 2s/t - v
So: s = vt - (1/2)at^2
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