Solve Kinematics Problem: Rocket Powered Sledge Speed in 60m Section

[ella_101]

Homework Statement

A rocket powered sledge accelerates at 35ms-2 and takes 1.6s to pass through a 60m section of a test track. Find the speed at which it entered the section what was its speed when it left?

Homework Equations

I think this is the equation to use x=ut + 1/2at2 and than use a=v-u/t to get v ?

The Attempt at a Solution

a= 35m/s
t= 1.6s
u=?
v=?
x= 60m

I got weird answers so there's no point putting them up!

please show your working

thanks

 

[malty]

Homework Statement

A rocket powered sledge accelerates at 35ms-2 and takes 1.6s to pass through a 60m section of a test track. Find the speed at which it entered the section what was its speed when it left?

Homework Equations

I think this is the equation to use x=ut + 1/2at2 and than use a=v-u/t to get v ?

The Attempt at a Solution

a= 35m/s
t= 1.6s
u=?
v=?
x= 60m

I got weird answers so there's no point putting them up!

please show your working

thanks

What exactly do you mean by a weird answer? Please put workings up, because your method seems right.

 

[ella_101]

when i make 'u' the subject of the forumal i got 65.5 ( which is wrong) and for 'v' I got 121.5

I think my teacher said the answer was 9.5 for u and v i don't know,

what did you get ?

 

[ella_101]

I know its an 'easy' question but i think i am just getting the equation wrong

 

[malty]

when i make 'u' the subject of the forumal i got 65.5 ( which is wrong) and for 'v' I got 121.5

I think my teacher said the answer was 9.5 for u and v i don't know,

what did you get ?

Teacher is right, just remember that experience is the best teacher so by making this mistake and figuring out where you made it you've learned more, than me simply showing you the solution.

If you want you can show me you workings step by step, but as far as I can tell your eq is right your just calculating it incorrectly.How did you get 65.5?

 

[ella_101]

okay,

x= ut + 1/2 at2

rearranged to give;

u= 1/2at2 + x/t ( this is were I think I am going wrong , rearranging it?)

than just plug in the numbers. = 65.5

OR
alternatively you can 'show' your working out=)

 

[tru_royalty]

Alternatively, I found you can use simultaneous equations:
(v+u)/2=s/t...So, v+u=75 (i)
Also, v=u+at...So, u=v-56 (ii)
Now, we have 2v-56=75, and v=65.5...u=9.5
That's a simpler, but more bothersome method...

 

[tru_royalty]

Your transposition is a little faulty... If s=ut+1/2at^2...Then u = (s-1/2at^2)/t...What you found was your final velocity, v...Since, s=vt-1/2at^2...v=(s+1/2at^2)/t...Go back over your steps in rearranging the equation, you'll see the mistake.