How much energy are you going to get out, and how far are you going to be able to drive a car with this expansion, let's say, so that's the problem.

你能获得多少能量，利用这次膨胀,你可以把你的车开出多远，比如说这就是问题所在。

麻省理工公开课 - 热力学与动力学课程节选

Car is traveling with some initial speed v0 in the horizontal direction.

车以 v0 的初速度沿水平方向开出

耶鲁公开课 - 基础物理课程节选