用40Ｎ的力拉一轻弹簧，可使其伸长0.10m。此弹簧下应挂_____kg的物体，才能使弹簧振子作简谐振动的圆频率10rad/s。

两个弹簧振子的振动周期都是0.4s。第一个振子从平衡位置向负方向运动时，第二个振子正处于正最大位移处，则第一个振子超前第二个振子______π的相位。

用余弦函数表示一质点的简谐振动方程，设其振幅为0.1米，频率为10赫兹。初相为0.5π，则t=0时刻，质点的速度大小等于____π m/s，加速度大小等于_____π m/s2。

一弹簧振子作简谐振动，若t = 0时，振子在负的最大位移处，用余弦函数表示振动表达式时，则振动初相为_____π。

物体运动时，它的位置按余弦函数的规律随时间变化，这种运动称为简谐振动。

A. 对
B. 错

弹簧振子的简谐振动频率与振幅有关，振幅越大，频率也越大。

A. 对
B. 错

一个弹簧振子作简谐振动时，它的机械能随时间按余弦规律变化。

A. 对
B. 错

A: Which do you prefer, tea or coffee?B: ________________.

A. Yes, I do
B. I prefer both
C. I prefer coffee to tea
D. No, I don't

What does a waiter/ waitress say to the guest when the restaurant is fully occupied?

A:If you wait in the lounge now, I’ll inform you when there’s a table for you.;
B:Sorry. But you arrive too late. The restaurant next to us is very good, too.;
C:I’m awfully sorry. There are no vacancies left now.;
D:Would you like to wait for a moment?;

What would a waiter/ waitress say when spilling wine on a guest and the table?

A:Here’s the cloth. Please clean it now.;
B:Sorry, sir. But could you make do with the table?;
C:I’m sorry, sir. I’ll clean the table immediately.;
D:Sorry, sir. We’ll clean your coat for free and send it back today.;