求：①甲对地面的压强p；

②若将乙叠放在甲的上方中央，乙对甲的压强为p₁，若将甲叠放在乙的上方中央，甲对乙的压强为p₂，已知p₂=4p₁．求乙的密度．

③当甲、乙分别平放在水平地面上时，若分别沿水平方向切去相同的体积V，则求甲、乙对地面压强变化量△p_甲与△p_乙的比值．

    The world renowned British Physicist Stephen Hawking who tried to explain the mysteries of the universe to millions of people passed away on March 14th, 2018 at the age of 76. His family said he died peacefully at his home in Cambridge. Professor Hawking used wheelchair and was able to speak only through a computer synthesizer(合成器), having been suffering from a rare form of motor neuron disease as a young man. Despite being given only a few years to live, he wrote popular science books for several decades. A film about his life The Theory of Everything won an Oscar for the actor Eddie Redmayne who portrayed him.

    Stephen's daughter Lucy spoke about her father's love of the limelight in 2012. She said, “Actually my father is also a showman. He loves a big show, a big stage and bright light, whether it's him on stage or whether it's watching the spectacle.”

    Stephen Hawking's death was announced in the statement by his children who said they will miss him forever. They said his courage and brilliance inspired people across the world. Many leaders from different countries paid tribute(致敬) to him including the Indian Prime Minister Narendra Modi, who said Professor Hawking had made the world a better place.