Rearranging acceleration formulas

[lornf]

Homework Statement

a=1.8m/s/s
v/sf=7.6m/s
u/si=?
t=2.5s

Find the initial speed[/B]

Homework Equations

a=v-u/t

The Attempt at a Solution

a=v-u/t
1.8=7.6-u/2.5
u=7.6+1.8/2.8
u=3.357...
u=3.36m/s

Is this correct? Sorry if the layout is messy this is my first time using it.

 

[kuruman]

v/sf=7.6m/s
u/si=?

Can you explain in plain English what these are?

 

[lornf]

Can you explain in plain English what these are?

v/sf is the final speed and u/si is the initial speed. Sorry our school teaches them in unconventional ways.

 

[Eclair_de_XII]

a=v-u/t

That's not dimensionally correct. $v$ does not have the same units as $a$ or $u/t$. You might want to take a look at your motion equations again.

 

[kuruman]

v/sf is the final speed and u/si is the initial speed. Sorry our school teaches them in unconventional ways.

It's OK, as long as we both understand what the symbols stand for. In your notation, the acceleration is $$a=\frac{v/sf-u/si}{t}$$ Can you solve this equation for $v/sf$?

 

[lornf]

It's OK, as long as we both understand what the symbols stand for. In your notation, the acceleration is $$a=\frac{v/sf-u/si}{t}$$ Can you solve this equation for $v/sf$?

Well without values, to rearrange the equation it would be -
a=v-u/t
v-u=at (a x t)
v=at+u

Is this what you mean? Did you want me to rearrange?

 

[kuruman]

That's what I mean, but why did you change your symbols? I thought you said the final velocity is v/sf and the initial velocity u/si. In any case, now that you have the final velocity on the left and the given quantities on the right, you can put in the numbers.

 

[lornf]

Ah sorry you've misunderstood one of my replies but it's fine since I understand now, thank you!

 

[kuruman]

I think I understand now. The "/sf" part is like a subscript and stands for "speed final". Similarly "/si" stands for "speed initial." The problem with this notation is that the slash "/" more commonly denotes division which is what @Eclair_de_XII 's reply was most likely based on.

 

[lornf]

Yes, I thought this was where the confusion was. Sorry for not explaining properly but again thanks for the help!