How much energy does it take to keep an object moving, compared to getting it moving?

Question

On a flat constant surface how much energy would it take one person to push a car from stationary to 5mph compared to the amount of energy required to keep it at 5mph?

I don't know if there is a relationship between these two values but I am hoping that if it takes 1 unit it of energy to keep the car moving then it would take 3 units of energy to get it moving (or something like that).

Answer 1

the difference is calculatable
m= mass of car
a= acceleration
d= distance traveled

work = F*distance = m*a*d
work to accelerate the car to 5mph
v^2 = u^2 + 2ad
E= 1/2mv^2
Force of Friction (Dynamic) = m*g*u
Total work = 1/2 mv^2 + m*g*u*d

case 2: at constant v=5mph, only the force to overcome the dynamic friction applies;
Total work = m*g*u*d;
5
Difference between moving a car from stationary vs keeping it at 5mph
5mph = 2.22m/s
Wdiff= 1/2 m * (2.22)^2

Answer 2

If there is no friction it would take no engery to keep the car moving at 5 mph. A body in motion tends to stay that way.

Now to find out how much engery it takes to keep the car going with friction.

Do the math to find out what it takes to accelerate the object to 5mph with no friction and measure the engery it takes with friction and subtract the second from the first.

The question of which takes more engery (with friction) depends on how long the car has to be kept at 5mph

Answer 3

Have you tried pushing a car ?

To get it moving and to overcome the friction between the tyres and the road, you may need help - a lot of energy expended.

Once moving the friction is much reduced and you can probably manage without further help .. unless it's uphill !

Answer 4

the energy would be equal to the friction from the surface and the air resistance... which depends on the type of surface, wind speed, etc. next question!

Answer 5

Little more energy than the force acting against it.

Answer 6

Depends on how much petrol is in the tank