Using your common sense to solve a physics problem.

riVeRraT, a bit of maybe not so common sense advice when dealing with equations.As long as you can, try NOT to put in any numbers in the equations. If it says that the mass of the car is 'm', use 'm' as long as you possibly can.It is also perfectly reasonable, and often prefered, to give an answer that isn't a number but just the final equation that you can just stick everything into.That means less mess with calculators and rounding off and such. Quite a lot of people seem to think numbers are easier to work with, but it's usually the other way when it comes to equations.If there is any step you feel you don't understand, or you get stuck, I can help you out if you send a PM. I don't think posting answers in this thread is the intent of the thread maker.

Oh, I'm too used to built in PM features; E-mailing would be equivalent.

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You mean I will role down a hill at the same speed regrdless of the slope? you obviously didn't understand how I was applying the grade to the formula.
  —RiVeRraT

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Acceleration due to gravity is constant. However, you will roll faster down a hill the steeper it is. This is because while the strenght of gravity is constant, it has a direction (toward the center of the earth). In a slope, it points partially into the ground and partially 'down' the slope.Note that regardless of how steep the slope is, gravity can only contribute from 0 to 9.8m/s^2 acceleration. If the slope is vertical, it's basically a free fall.I think you got the right idea but expressed it strangely.Same with the Uk bit. Uk itself is constant (given in the problem). It's the force between the car and the road that can change.Also, your initial speed formula is off. You need to take the square root of that to get v.The formula starts as v^2 = 2*g*d*Uk. You should always double-check the units (v must be m/s). g*d is in m^2/s^2.This is a perfectly good formula for flat ground, but it's probably better to start from scratch instead of modifying it when you have a slope.This message has been edited by Melchior, 09-24-2004 02:24 PM

The answer for flat ground, Uk=0.45, d=30 meters is;v^2 = 2*Uk*g*d = 264.6 m^s/s^2v = 16.267 m/s16.267 m/s = 16.267 / 1609 * 3600 mph = 36.396 mphGiven that there are 1609 meters in a mile, and 3600 seconds in an hour.

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which carries a uniform line charge of λ.

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Lambda is a rather frequent symbol and you can't really assume it means wavelenght unless you are talking about wave-physics or similar fields.This message has been edited by Melchior, 09-27-2004 05:04 PM