A Suvat

[KevinE]

Hi guys this isn't an assignment or homework I'm just studying.
I know the answers are 1.1m/s/s
and 5m/s.
I'm just wondering how to get to it?

So...

The distance
s meters traveled by a vehicle is given by the formula

s=ut + 1/2 at^2

s= 20 meters when t is 3 secs
s= 50 meters when t is 6 secs


Calculate the values for the initial velocity u
and the acceleration a

 

[KevinE]

I thought maybe because there was two sets of values and two unknown variables it might be a simultaneous.

I set plugged in the numbers and simplified to

20 = 3u + 3a
50 = 6u + 18a

120 = 18u + 18a
50 = 6u + 18a

70 = 12u

u = 5.83

This is obviously incorrect - But how to solve for two unknown variables at once - a mystery is what it is

 

[Ishuda]

I thought maybe because there was two sets of values and two unknown variables it might be a simultaneous.

I set plugged in the numbers and simplified to

20 = 3u + 3a
50 = 6u + 18a

120 = 18u + 18a
50 = 6u + 18a

70 = 12u

u = 5.83

This is obviously incorrect - But how to solve for two unknown variables at once - a mystery is what it is

You method is correct, it is just that you made an early mistake (see above in red). That should have been
20 = 3 u + 4.5 a
which leads to
u = 5 and a ~ 1.1

 

[KevinE]

Thanks guys I thought I was way off so I did not bother to recalculate, there in lies the problem, I suppose. Anyways thanks once again. I would be at a loss without you.