1. I find that it is difficult to learn English well, so I mu.st study harder.

    I find ______difficult_______ _____English well,so I must study harder.

2. He didn't get married until he was in his thirties.

    It was______ _______he was in his thirties ______he got married.

3. We started early so that we could arrive there before 8 o'clock.

    We started early_______ ______ _______arrivethere before 8 o'clock.

4. They hurried up because it was getting dark.

     ________ __________ because it was getting dark _______ they hurried up.

5. It's mad of you to go there alone in such bad weather.

    ________ ________ ________you to go there alone in  such bad weather.

如图所示，木块重60N放在倾角为37°的固定斜面上，用F=10N的水平力推木块，木块恰能沿斜面匀速下滑，求：

（1）木块与斜面间的摩擦力大小

（2）木块与斜面间的动摩擦因数（sin37°=0.6，cos37°=0.8）