First, if the pulley is massless, M vanishes;

首先如果滑轮质量为 0 M 就等于 0
forget it downstairs.

分母中就没有这一项了
Cancel m with m and you get a=g;

上下约去 m 就可以得到 a=g
that's the correct answer.

这是正确的答案
It's just falling down freely.

它就这么自由下落
Now, I'm going to subject it to another stringent test.

现在我要对结果做一些更为严格的检验
Suppose I ask you-- Suppose it's got a distance h through which it can fall.

如果我问你假如它从高为 h 处开始下落
How fast is the block moving when it hits the ground?

当它落地时速度是多大
Just before it hits the ground, what's the velocity?

就在它撞地前的那一瞬间速度是多大
So, you have to think about what ideas you'd invoke to do that.

你应该想一想应该用到哪些知识来解决问题
Is the acceleration constant, first of all?

首先加速度是常数吗
Yes? Gentleman in the back said "yes."

请讲后面的先生说"是"