Thanh AB đồng chất dài 1 m khối lượng 1,5 kg được giữ cân bằng
nằm ngang bởi bản lề A và dây BC như hình vẽ. = 60 0 , lấy g=10 m/s 2 .
a) Tính momen của trọng lực của thanh AB và momen của lực căng dây
đối với trục quay A.
b) Tính cánh tay đòn của lực căng dây
c) Tính lực căng dây.
13. Over millions of years, the forceful rush of water can cut deep canyons into dry desert rock.________ Grand Canyon, in Arizona, for example, was carved by water.
a. A b. An c. The d. no article
14. Mr. Pike works hard and spends more economically to make ________ for his old age.
a, provide b. provision c. provider d. provident
15. Only a very delicate thermometer can measure such tiny changes in________
a. water b. temperature c. current d. marine
16. They spent their childhood in a tiny fishery village by the sea.
a. small b. big c. large d. enormous
17. Seventy-five percent of the earth ________ are covered by seas and oceans.
a. face b. flat c. resurface d. surface
18. Oil spills are a great a great ________ to the undersea world.
a. threat b. threaten e. threatened d. threateningly
19. Her work has enormously contributed ________ the charity collection.
a. for b. on c. to d. in
20. John’s father is a ________ scientist. He studies life in the sea.
a. marine b. undersea c. submarine d. organism
I. Choose the word which is stressed differently from the rest.
1. a. mystery b. century c. oxygen d. submarine
2. a. activity b. investigate c. diversity d. fertilizer
3. a. mammal b. human c. beneath d. secret
4. a. oversize b. satellite c. existence d. pesticide
5. a. plastic b. concern c. carry d. reason
II. Choose a, b, c, or d that best completes each unfinished sentence; best substitutes the underlined part; or has the same meaning to the sentence above.
6. Sperm whale populations are at risk due to hunting.
a. in danger b. at hand c. on purpose d. in use
7. The blue ________ is the largest known animal ever to have lived on sea or ! and. a. krill b. tuna c. whale d. shell
8. Green turtles can migrate more than 1400 miles to ________ their eggs.
a. lie b. lay c. laid d. lain
9. Sea life has a strong ________ on the composition of sea water.
a. challenge b. information c. investigation d. influence
10. There is a wide variety of opinions on sea food cultivation.
a. same b. diversity c. supply d. interaction
11. The sea bottom is________ into three areas: the continental shelf, the continental slope, and the ocean floor.
a. divided b. changed c. consisted d. included
12. If you pour oil on water, it will ________
a. float b. drown c. dissolve d. compound