题干

物体静止在光滑水平面上,对物体施一水平向右的恒力F1,经过时间t突然撤去F1,立即对它施一水平向左的恒力F2,又经过时间t 物体恰好到达出发点。下列说法正确的是(  )

A:水平恒力F1和F2大小之比为1:2

B:刚撤去F1时刻和恰好回到出发点时刻物体的速率之比为1:3

C:F1和F2对该物体做功之比是1:3

D:F1、F2对该物体做功的最大功率之比是1:3

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C

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    Whether you're up for a Crocodile Dundee's adventure or you'd just like a taste of the Australian sun, the beaches in and around Sydney can offer you all that and more.

Sydney Beach

    Sydney Beach is located at Sydney's northernmost tip on an extension(延伸) of land ending at Palm Beach. Before checking out the golden sand, take a quick tour of the houses of millionaires from the art and film industries.

Palm Beach

    Only about an hour from downtown Sydney, Palm Beach offers a long stretch(延伸) of clean sand and water. With parking near the center of the beach, that leaves the rest of it as a peaceful location with a sparse population, from which you can go surfing but take care — without the huge crowds of other Sydney's beaches, Palm Beach doesn't afford quite the safety level to be found elsewhere. Volunteer lifesavers are on duty only on weekends and holidays.

Bondi Beach

    For the famous beach, Bondi Beach has to be your choice. Parking is difficult to find even on slow days, so consider taking public transport to this world—known beach in the eastern Sydney suburbs. Easily reachable by taxi, bus, and rail, Bondi Beach offers sun bathing, swimming, snorkeling, and all sorts of water sports fun. If you're in the mood for a bit of exercise, two scenic coastal walks will afford you great views and sights along the shore. Take in views from Mackenzie's Point. It starts at Bondi and heads south to Bronte Beach. But don't try to swim in Mackenzie's Bay — it holds dangers such as hidden rocks.

Bronte Beach

    Your second choice for a scenic coastal walk covers a few miles and takes you from Bronte Beach to Waverly Cemetery, where many famous Australians are buried, including the poet Henry Lawson.