A carriage is caused to move along a straight railway line by a constant force F given by F=i+2j+3kN . If the train moves from an initial point ri to a final point rf where
ri= i+ 7j m
rf= 4i - j m
calculate the amount of work W done by this force. Find also the angle between these position vectors.
answers: W= 19J angle= 95.9
Vectors
2008-08-02 11:46 pm
回答 (1)
2008-08-03 6:04 am
✔ 最佳答案
I think that F should be i-2j 3k in order to get your answerr = rf - ri = (4i - j ) - (i 7j) = 3i - 8j
W = F dot r = (i - 2j 3k) dot (3i - 8j) = 3 16 = 19J
angle = arccos [(ri dot rf)/(|ri| rf|)]
= arccos ([(4i - j ) dot (i 7j)]/[sqrt(50)sqrt(17)])
= arccos (-3/29.154) = 95.9 degree.
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https://hk.answers.yahoo.com/question/index?qid=20080802000051KK01592