为了增强体能，全班同学进行爬楼梯训练．体重500N的小刚在10s内连续爬楼梯的总高度为7m．求：
（1）小刚爬楼梯所做的功．
（2）小刚爬楼梯的功率．
小刚爬楼梯所做的功：
W=Gh=500N×7m=3500J，
小刚爬楼梯所做功功率：
P=
=W t
=350W．3500J 10s
答：（1）小刚爬楼梯所做的功为3500J；
（2）小刚爬楼梯的功率为350W．
Harry Potter is a set of popular books created by J.K.Rowling in Britain. The books tell us some stories about a talented wizard (天才魔法师), Harry Potter. When he was eleven years old, he had an unhappy life. However, a strange letter changed everything. It said he was accepted by Hogwart's magic school which was closed to the common people. All kinds of adventures (冒险) happened to Harry from then on. He met Ron Weasley and Hermione Granger on his way to school. They became good friends later. Harry did well in his lessons and worked hard to play magic. Harry always had a positive attitude(态度)when he faced the difficulties. With the help of his friends, he tried his best to beat the enemies. Finally, the world peace came back. Smile appeared on everyone's face. If someone wants to know what takes place in the magical world, he will have to read the set of books by himself!
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