00:01
In this question we have a railroad freight car that's going to roll down an incline and collide with a stationary train.
00:09
This railroad freight car has a frictional force acting on it from its brakes and we are going to perform a number of calculations regarding forces and energy and dealing with the collision.
00:27
So we're given this interesting unit for the incline of three over a thousand which means each one thousand meters of travel corresponds to a height change of three meters.
00:40
So for our train traveling two thousand meters down the incline it will experience a drop of six meters and i want to point something out that's going to help with our calculations.
00:52
The way this slope is expressed is a little bit different than what we usually deal with in usually we're dealing with an angle theta either from the vertical or from the horizontal, in this case horizontal, and we would talk about our slope in terms of you know sines and cosines of that angle.
01:19
Well what we're given here is an opposite side of the triangle and a hypotenuse so we can say that the sine of our angle is equal to this slope when it's expressed as per one thousand or even as a decimal.
01:38
So here it'd be sine theta equals 0 .003, it means three thousandths.
01:43
We're going to be able to use that to do some substitutions later on in the question.
01:50
So in part a what is the maximum slope given in per thousand that a one kilonewton braking force can keep the stationary and we're going to show that the one kilonewton braking force is not enough to hold it on this three per one thousand incline.
02:05
So to stay stationary that means that our net force is equal to zero, there's no acceleration...