# Sorry, I need help again

1. Oct 13, 2004

### dabouncerx24

The problem is, a 1000kg car pulls a 450kg trailer. The car exerts a horizontal force of 3500N against the ground in order to accelerate. What force does the car exert on the trailer? Assume a friction coefficient of 0.15 for the trailer.

2. Oct 13, 2004

### christinono

You need to either add the frictional force to the 3500N or subtract it. The frictional force equals (0.15)(mg) or (0.15)(450)(9.81).

3. Oct 13, 2004

### dabouncerx24

I don't get why adding the friction force to 3500N is logical? Can you plz explain it to me.

4. Oct 13, 2004

### Pyrrhus

Do the forces analysis...

5. Oct 15, 2004

### dabouncerx24

Well I figured out that problem.

Here is another one, please assist me.

At an accident scene on a level road, investigators measure a car;s skid mark to be 88m long. It was a rainy day and the coefficient of friction was estimated to be 0.42. Use these dta to determine the speed of the car when the driver slammed on the brakes (why does the car's mass not matter).

So far I figured I would use Fd=KE-KE' so all the ms will cancel each other.