question.

Question

question.

idku · Answer

If friction (rolling friction and air drag) results in a
retarding force of $294~\rm N$ at a speed of $50~\rm km/h$,
what is the minimum energy needed to move the car
a distance of $287~\rm m$,  at a constant speed of 50 km/h?

kanwal32 · Answer

is the weight of the car given

idku · Answer

The weight of the car:  1228-kg
(Sorry that I left this out)

kanwal32 · Answer

so the answer is E-ForceXdisplacment=1/2mv^2

kanwal32 · Answer

put in the values

kanwal32 · Answer

and convert it into m/s

idku · Answer

$E - F\times x=\frac{1}{2}mv^2$         ?

So, basically   $\Delta E=\frac{1}{2}mv^2$   ?

idku · Answer

Wait, no, that is work....

kanwal32 · Answer

the energy supplied=1/2mv^2+Force*displacement

idku · Answer

Oh

idku · Answer

50 km/h = 13.89 m/s

E = (1/2)(1228 kg )(13.89 m/s )^2+(294 N)* (287 m)

idku · Answer

Like this?

kanwal32 · Answer

yeah

idku · Answer

alright will see if this is right...
tnx for helping me out:)

idku · Answer

I converted to KJ (killo Joules), and I have
202.840 KJ

but the site tells me it is wrong

kanwal32 · Answer

man i think it should be right

idku · Answer

I checked it, and it's wrong:(
Don't know why.

Maybe the formula is off?

kanwal32 · Answer

can u send me the link

idku · Answer

It is a flipit-physics homework

idku · Answer

I don't think I can link you to this, because you don't have the course-access.

kanwal32 · Answer

man i am sure it is right

idku · Answer

But that is precisely the question:

If friction (rolling friction and air drag) results in a retarding force of 294 N at a speed of 50 km/h, what is the minimum energy needed to move the car a distance of 287 m at a constant speed of 50 km/h?

And from the previous part I know the mass of the car:  1228 kg.

kanwal32 · Answer

the work done by the friction is force*displacement
sorry

kanwal32 · Answer

pls check 84.378

idku · Answer

we accounted for that, didn't we?
E = (1/2)(1228 kg )(13.89 m/s )^2+$\color{red}{(294 N)* (287 m)}$

kanwal32 · Answer

kilo joules

idku · Answer

Wow, that was right.
How did you get this answer ?

kanwal32 · Answer

man i forgot that the energy in the system remains constant

kanwal32 · Answer

1/2mV^2=E+1/2mv^2-force*displacement

idku · Answer

Oh, I get it ...

idku · Answer

So it just results in Force × Displacement

idku · Answer

Thanks again!