题目

The Internet has led to a huge increase in credit card (信用卡) fraud. Your card information could even be for sale in an illegal web site. Web sites’ offering cheap goods and services should be regarded with care. Online shoppers who enter their credit card information may never receive the goods they thought they bought. The thieves then go shopping with your card number or sell the information over the Internet. Computers hackers have broken down security systems, raising questions about the safety of cardholder information. Several months ago, 25,000 customers of CD Universe,（10分）如图所示，高为h＝1.25m的平台上，覆盖一层薄冰，现有一质量ｍ="50" kg的滑雪爱好者，以一定的初速度从平台边缘水平滑出，着地时的速度方向与水平地面的夹角为45°（不计空气阻力，滑雪者可视为质点，取g＝10m/s2）。求：（1）滑雪者在空中运动的时间；（2）滑雪者着地点到平台边缘的水平距离；（3）滑雪者着地时重力做功的瞬时功率。