题目

听下面一段对话，回答问题。 （1） Why didn't the man recognize the woman's voice? A . She hasn't contacted him for long B . She played a joke on him C . She suffered from sickness （2） What does the man want to borrow? A . Some glasses. B . Some sugar. C . Some cold beers （3） What is the man preparing for? A . A festival B . A party C . A dinner质量为5kg的物体静止在水平桌面上，当受到20N的水平推力作用时恰好开始滑动，物体和桌面的动摩擦因数为0.36．则当水平推力为15N而物体静止时，物体受到的摩擦力大小为 N；当水平推力为40N时，物体受到的摩擦力大小为 N．（ g=10m/s2）