题干

某学习小组使用几个相同的滑轮分别进行机械效率的测定,如图.他们将测得钩码重G、拉力F、钩码上升的髙度h、测力计移动的距离S,并将计算出的有用功W有用、总功W和机械效率η数据一并记入下表:

实验

G/N

F/N

h/m

s/m

W有用/J

W/J

η

1

2

2.1

0.1

0.1

0.2

0.21

95.2%

2

2

1.2

0.1

0.2

0.2

0.24

83.3%

3

2

0.9

0.1

0.3

0.2

0.27

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    My father was always a good gardener. One of my earliest memories is standing without shoes in the freshly tilled soil, my hands blackened from digging in the ground.

    As a child, I loved following Dad around in the garden. I remember Dad pushing the tiller(耕作机) ahead in perfectly straight lines. Dad loved growing all sorts of things: yellow and green onions, watermelons almost as big as me, rows of yellow corn, and our favorite — red tomatoes.

    As I grew into a teenager, I didn't get so excited about gardening with Dad. Instead of magical land of possibility, it had turned into some kind of prison. As Dad grew older, his love for gardening never disappeared. After all the kids were grown and had started families of their own, Dad turned to gardening like never before. Even when he was diagnosed with cancer, he still took care of his garden.

    But then, the cancer, bit by bit, invaded his body. I had to do the things he used to do. What really convinced me that Dad was dying was the state of his garden that year. The rows and rows of multicolored vegetables were gone. Too tired to weed them, he simply let them be. He only planted tomatoes.

    For the first few years after he died, I couldn't even bear to look at anyone's garden without having strong memories pour over me like cold water from a bucket. Three years ago, I decided to plant my own garden and started out with just a few tomatoes. That morning, after breaking up a fair amount of soil, something caught the corner of my eye and I had to smile. It was my eight-year-old son Nathan, happily playing in the freshly tilled soil.