Work And Power Problem

[DethRose]

Hey this is my last work and power problem haha...this is the hardest of them all.

the question is


A tractor pulls a loaded sled, massing 4110 kg, along a level snow packed road at a constant speed of 45 km/h. If the amount of friction between the road and the sled is 585 N find the power required.


I found the weight of the load in newtons to be 40319.1 Nand subtracted the friction to get a net force of 39734.1 N but i dont know how to find the power from here.


help please

[Andrew Mason]

A tractor pulls a loaded sled, massing 4110 kg, along a level snow packed road at a constant speed of 45 km/h. If the amount of friction between the road and the sled is 585 N find the power required.

I found the weight of the load in newtons to be 40319.1 Nand subtracted the friction to get a net force of 39734.1 N but i dont know how to find the power from here.I am not sure why you are doing that. The mass of the sled is irrelevant since you know the actual force of friction.

Power is: Work (against the friction force) / unit time. Work is: Force (friction) x distance. So power is Force (friction) x distance/unit time = Force (friction) x speed.

AM

[mjfairch]

Make sure you use consistent units as well. If you're going to use Newtons, then you need to use m/s as well instead of km/hr. More generally, for reasons pointed out by Andrew Mason, power is given by:

P=\vec F \cdot \vec v = |\vec F| |\vec v| \cos{(\theta)}