题干

如图所示,一根光滑的轻杆水平放置,左端o处连接在竖直的转轴上,a、b为两个可看做质点的小球,穿在杆上,并用细线分别连接oa和ab,且oa=ab,已知b球质量为a球质量的2倍。当轻杆绕轴在水平面内匀速转动时,oa和ab两线的拉力之比为

A:2∶1

B:1∶2

C:5∶1

D:5∶4

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D

同类题5

阅读理解

B

    “Can I take your order?”Night after night.I had to say this as l worked in my family's restaurant.My father was a fantastic cook.He wanted me to cook with him.but I didn't like cooking.Because of the restaurant, my father was always busy.He never had time to play soccer with me.

    During my high school and college years,I worked with my family at night.But I always avoided the kitchen.I couldn't wait to graduate (毕业),so I could move away from the family business(生意).Several days before my graduation day, my father and I started looking at new cars.Finally, we found the right car.I was sure that my father would give it to me as my graduation gift.

    On my graduation day, my father gave me a book as a gift.It was his old cookbook.I was so angry that I gave it back to him and ran out of the house.I soon moved away and started my own business.Although I often saw my father during holidays,we never talked about the graduation gift.Then one day, I got a call that my father was sick.I went to see him because l was very worried.

    That night, I looked through my father's books and saw the cookbook that he had given me years before.I carefully opened the cookbook and went through it.Then I found something that made me cry.It was a check(支票)for$30,000 dated(注有日期)the day of my graduation.And the price of the car my father and I chose all those years ago was $30,000.