# Homework Help: The speed of the car

1. Feb 14, 2013

### nody

1. The problem statement, all variables and given/known data
A car is driving 25km/h upward a road,the road is under a angle of 4 degrees.The same car goes 100 km/h when it goes downward the same road,in both cases,when the car is driving upward and downward it's using the maximum possible power of the motor.Whats the speed of the car when it's driving on a straight road(the angle is 0).

2. Relevant equations
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html .Equations for motion.

3. The attempt at a solution[/b
I know from real life that if a road is 4 degrees this means that after 100 meters on the straight ground you go 4 meters up.So I thought it's a triangle and I used pitagoras equation to get the hypothenuse.After I got that I thought ok,now we have the way which the car has overcome.And I thought also that because it's using full motors power that the speed should be constant,but I don't know how to continue or if the previous things which I said here are correct.

2. Feb 14, 2013

### voko

4 degrees does not mean 4 meter elevation per 100 m, it is more. What is the equation for that?

Regardless, you should start by writing down the forces acting on the car; their sum is the acceleration, which is zero. You have three different cases to consider.