# Homework Help: Forces, Friction and Slopes

1. Mar 5, 2008

### robdude

Hi all,

Let me first apologize for the nature of my post. If this sort of thing isn't welcome here, just say the word. The truth is, I haven't touched physics since my second year of high school (that was many years ago, I went on to college a Comp Sci major, graduated). And yet, here I am, doing homework. :)

Long story short, my girlfriend has a homework assignment that is due at midnight (less than 30 minutes). She is sick and only finished about half of the assignment before going to bed. For the last three hours I've been trying to do her homework for her. It's been going good, but very, very slowly. I have two questions remaining and so far, I'm averaging one question every hour or so.

If someone could help me finish this problem, I would be eternally grateful. I'm not sure what level of traffic this site gets, if this post is more than 30 minutes old when you see, no sense in wasting your time. But if you see this right away and can do these sorts of things....

If 15.0 HP are required to drive a 1900-kg automobile at 60.0 km/h on a level road, what is the total retarding force due to friction, air resistance, and so on?

671 N (This is correct and was as far as I've gotten so far...)

What power is necessary to drive the car at 60.0 km/h up a 10.0% grade (a hill rising 10.0m vertically in 100.0m horizontally)?

What power is necessary to drive the car at 60.0 km/h down a 1.00% grade?

Down what percent grade would the car coast at 60.0 km/h?