【简答题】Many people think a telephone is essential. But I think it is a pest and a time waster. Very often you find it impossible to escape from some idle or curious chatter-box, or from somebody who wants so...
【单选题】You toss a 0.150-kg baseball straight upward so that it leaves your hand moving at 20.0 m/s. The ball reaches a maximum height y2. What is the speed of the ball when it is at a height of y2/2? Ignore ...