A car accelerates uniformly from +10.0 m/s to +40.0 m/s over a distance of 125 m. How long did it take to go that distance? Show all your work, including the equation used, given and unknown quantities, and any algebra required. Make sure your answer has the correct number of significant figures.

Question

ganeshie8 · Answer

kinematics ?

anonymous · Answer

@ganeshie8  yes. please help me.

ganeshie8 · Answer

first start by putting down whats given

ganeshie8 · Answer

A car accelerates uniformly from +10.0 m/s to +40.0 m/s over a distance of 125 m

initial velocity u = 10
final velocity  v  = 40
distance    s = 125

ganeshie8 · Answer

t = ?

ganeshie8 · Answer

which equations we can use ?

ganeshie8 · Answer

any ideas ?, u have v, u, s and u want t

anonymous · Answer

isnt initial velocity vi? and final velocity is vf?

anonymous · Answer

@ganeshie8  vi=10.0, 
vf=40.0, 
deltax(distance)=125 
t: ?
formula: delta d =1/2(vi+vf) delta t  
125/ ½  (10.0+40.0) 
= 5.0 sec

anonymous · Answer

am i right?

ganeshie8 · Answer

hey no, we need to use kinematics equations

ganeshie8 · Answer

v^2-u^2 = 2as

ganeshie8 · Answer

saw this equation before ? :)

anonymous · Answer

ohh... um no I havent

anonymous · Answer

so what is v^2 and u^2 and as?

ganeshie8 · Answer

a is acceleration
s is distance travelled

v and u  are final/initial velocities

anonymous · Answer

ok... what about the =2as?

ganeshie8 · Answer

sorry, thats 2*a*s

ganeshie8 · Answer

v^2-u^2 = 2as

40^2-10^2 = 2*a*125

solve a first

ganeshie8 · Answer

once u have a, 
use below equation to find time, t

v = u+at

ganeshie8 · Answer

give it a try :)

anonymous · Answer

so it 10.0^2 * 40.0^2= 1700

ganeshie8 · Answer

v^2-u^2 = 2as

40^2-10^2 = 2*a*125
1600 - 100 = 250a

ganeshie8 · Answer

solve a, can u ? :)

anonymous · Answer

@ganeshie8 ummm whats a?

ganeshie8 · Answer

a = acceleration

anonymous · Answer

it doest give acceleration on the question

anonymous · Answer

v^2-u^2 = -1500

ganeshie8 · Answer

v^2-u^2 = 2as

40^2-10^2 = 2*a*125
1600 - 100 = 250a
1500 = 250a
1500/250 = a
6 = a

so, the acceleration a = 6

ganeshie8 · Answer

Now that we have acceleration a = 6,
we can use below equation to find time, t

v = u+at

ganeshie8 · Answer

v = u+at
40 = 10+6t

anonymous · Answer

oh i thought it would be 10.0^-40.0^2

ganeshie8 · Answer

solve t

ganeshie8 · Answer

haaah i see that :) thats why ive put the entire solution, so that it becomes clear to u :)

ganeshie8 · Answer

u still need to solve t in above equation

anonymous · Answer

ok 10+6 = 16...

ganeshie8 · Answer

DONT ignore the 't' attached to 6

ganeshie8 · Answer

v = u+at
40 = 10+6t

subtract 10 both sides

30 = 6t

divide 6 both sides

5 = t

t  = 5

ganeshie8 · Answer

so, it takes  5 seconds to go to t hat distance of 125 meters

ganeshie8 · Answer

see if it makes some sense

anonymous · Answer

I had 5 as my answer earlier...

ganeshie8 · Answer

good :) 
5 = $\checkmark$

anonymous · Answer

why did you say my answer was wrong in the first place.

ganeshie8 · Answer

oh we both got same answers, weird

ganeshie8 · Answer

lets see

ganeshie8 · Answer

Your method :-
```
 vi=10.0, 
vf=40.0, 
deltax(distance)=125 
t: ?
formula: delta d =1/2(vi+vf) delta t  
125/ ½  (10.0+40.0) 
= 5.0 sec 
```

anonymous · Answer

yes i got 5

ganeshie8 · Answer

Yup ! im still thinking why ur method worked

anonymous · Answer

lol

ganeshie8 · Answer

-_- have to think, looks like uniform acceleration has something to do wid it

anonymous · Answer

whats the namw of the formula you gave me? v^2-u^2=2ac

anonymous · Answer

name*

ganeshie8 · Answer

thats 

v^2-u^2=2as

ganeshie8 · Answer

they're kinematics equations, u may google

anonymous · Answer

okay i will

ganeshie8 · Answer

lets get back on this ltr, to see why ur method worked  :)

anonymous · Answer

ok