Twenty years ago, I drove a taxi for a living. One night I went to pick up a passenger at 2:30 AM. When I arrived there, I walked to the door and knocked, “Just a minute,” answered a weak, elderly voice.
After a long pause, the door opened. A small woman in her eighties stood before me. By her side was a small suitcase. When we got into the taxi, she gave me an address, and then asked, “Could you drive through downtown?”
“It's not the shortest way,” I answered quickly.
“Oh, I'm in no hurry,” she said. “I'm on my way to a hospice(临终医院). I don't have any family left. The doctor says I don't have very long.”
I quietly reached over and shut off the meter(计价器).
For the next two hours, we drove through the city. She showed me the building where she had once worked, the neighborhood where she had lived, and the furniture shop that had once been a ballroom where she had gone dancing as a girl.
Sometimes she'd ask me to slow down in front of a special building and would sit staring into the darkness, saying nothing. In the early morning, she suddenly said,” I'm tired. Let's go now.”
We drove in silence to the address she had given me.
“How much do I pay you?” she asked.
“Nothing.” I said.
“You have to make a living,” she answered. “Oh, there are other passengers,”I answered.
Almost without thinking, I gave her a hug(拥抱). She held on me and said, “You gave an old woman a little moment of joy.”
知B轮的半径是A轮半径的2倍，当A轮边缘上各点的加速度大小为a时，则B轮边缘上各点的加速度大小为（两轮间不打滑）