Net Force of object changing velocity

[ital_dj]

[SOLVED] Net Force of object changing velocity

Hi, I'm studying for a test, so there might be a few of these in the next hour or so.

Homework Statement

A supertanker of mass 1.0 X 10$$^{8}$$ kg travels 3.5km, reaching a speed of 4.1km/h from rest. What was the magnitude of the unbalanced force acting on it?

Homework Equations

Fnet = ma
v$$^{2}_{2}$$ = v$$^{2}_{1}$$ + 2a$$\Delta$$d

The Attempt at a Solution

I tried (4.1km/h)$$^2$$ = 2a(3.5km)
$$\frac{16.81km/h^2}{3.5km}$$ = 2a
4.80km = 2a
2.4km/h = a

and then I tried converting it by dividing it by 60 twice, and sliding to the right 3 decimal places, then inserting it into the Fnet = ma.

I'm really stuck, and that's not good if I have a unit test tomorrow

 

[rock.freak667]

When using F=ma, you need m to be in kg and a to be in m/s^2
So, convert the velocities into m/s and the distance into m

 

[ital_dj]

I'll try it again but instead beforehand.. I did it after, though, does that make a difference?
EDIT: still not working out though.

 

[rock.freak667]

I'll try it again but instead beforehand.. I did it after, though, does that make a difference?

Not really but it seems correct that $a=2.4kmh^{-2}$. Just multiply by 1000 and divide by 3600 and it should be correct.

 

[ital_dj]

The answer in the book is 1.9 * 10$$^4$$

By multiplying 2.4 times 1000 and dividing by 3600 gives me 0.67. Still not correct. :S

 

[rock.freak667]

The answer in the book is 1.9 * 10$$^4$$

By multiplying 2.4 times 1000 and dividing by 3600 gives me 0.67. Still not correct. :S

Divide by 3600^2 . Sorry,told you to do the wrong thing.

 

[ital_dj]

OK Thanks.