At noon,ship A is 28km due west of a lighthouse L.The ship sails in the direction N20E.After 3 hour,it reaches port B,which is due north of the lighthouse.
(B).Find the shortest distance between the ship and the lighthouse.
(C).when will the ship be nearest to the lighthouse?
F4 MATH
2009-05-05 1:13 am
回答 (1)
2009-05-05 2:15 am
✔ 最佳答案
(B)the shortest distance=28cos20=26.3km
(C)
By the given , after 3 hour,it reaches port B,which is due north of the lighthouse
the distance between B and the starting point=28/sin20=81.9km
the speed of the ship=81.9/3=27.3km/h
when the ship reaches the point which is the nearest to the lighthouse ,
the distance travelled by the ship=28sin20=9.58km
time used=9.58/27.3=0.351 hour
i.e. the ship reaches the nearest to the lighthouse 0.351 hours later
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