# Need help with problem please

1. Jan 11, 2005

### darkys

a car is driven at a constant speed of 76km/h down a road. The car's engine delivers 48 kW of power. Calculate the average force that is resisting the motion of the car

any help would be appreciated. I had an idea, but i dont know if its right.

2. Jan 11, 2005

### Curious3141

What is the relationship between Power, force and velocity ?

3. Jan 11, 2005

### darkys

well i was thinking power=w/t, so power=fd/t, d/t is velocity, so power = force x velocity, and i figure out that force. it is asking for resisting force, so it is asking for the frictional force. Since it is constant speed, the net force is zero, so it would just be the negative force of the above force. This is what i was thinking

4. Jan 11, 2005

### Curious3141

Well, there you go.

Another way to look at it would be that all the engine's power is going to overcome friction. This is why the car is not accelerating.

Last edited: Jan 11, 2005
5. Jan 11, 2005

### darkys

thats right?

6. Jan 11, 2005

### brewnog

Yup yup!

Hmm, 'yup yup!' is too short, so I had to add this bit.