Tốc độ chuyển động - Bài tập nâng cao

Home Lớp 7 Khoa học tự nhiên 7 - Sách kết nối tri thức Bài 8: Tốc độ chuyển độngBài tập nâng cao

{"common":{"save":0,"post_id":"5996","level":3,"total":10,"point":10,"point_extra":0},"segment":[{"id":"9378","post_id":"5996","mon_id":"1158739","chapter_id":"1158740","question":"M\u1ed9t xà lan \u0111i d\u1ecdc b\u1edd sông trên quãng \u0111\u01b0\u1eddng AB v\u1edbi v\u1eadn t\u1ed1c 15 km\/h. N\u1ebfu t\u0103ng v\u1eadn t\u1ed1c thêm 3 km\/h thì xà lan \u0111\u1ebfn B s\u1edbm h\u01a1n d\u1ef1 \u0111\u1ecbnh 10 phút. Quãng \u0111\u01b0\u1eddng AB là:<\/p>","options":["A. 5 km."," B. 10 km.","C. 15 km.","D. 20 km."],"correct":"3","level":"3","hint":"S\u01b0\u0309 du\u0323ng công th\u01b0\u0301c:  $t = \\frac{s}{v}$<\/span> Th\u01a1\u0300i gian d\u01b0\u0323 \u0111i\u0323nh = th\u01a1\u0300i gian \u0111i + th\u01a1\u0300i gian \u0111ê\u0301n s\u01a1\u0301m h\u01a1n d\u01b0\u0323 \u0111i\u0323nh<\/p>","answer":"\u0110ô\u0309i $10 phu\u0301t = \\frac{1}{6}   (h)$<\/span><\/p>Th\u01a1\u0300i gian xa\u0300 lan \u0111i d\u1ecdc b\u1edd sông trên quãng \u0111\u01b0\u1eddng AB v\u1edbi v\u1eadn t\u1ed1c 15 km\/h la\u0300 $t_{1} = \\frac{AB}{15}   (h)$<\/span><\/p>Th\u01a1\u0300i gian xa\u0300 lan \u0111i d\u1ecdc b\u1edd sông trên quãng \u0111\u01b0\u1eddng AB v\u1edbi v\u1eadn t\u1ed1c 15 + 3 = 18 km\/h la\u0300 $t_{2} = \\frac{AB}{18}   (h)$<\/span><\/p>Vi\u0300 khi t\u0103ng vâ\u0323n tô\u0301c thêm 3 km\/h thi\u0300 xa\u0300 lan \u0111ê\u0301n B s\u01a1\u0301m h\u01a1n 10 phu\u0301t nên $t_1 - t_2 = \\frac{AB}{15} - \\frac{AB}{18} = \\frac{1}{6}(h) $<\/span><\/p>$\\Rightarrow AB({\\frac{1}{15} - \\frac{1}{18}}) = \\frac{1}{6} \\Rightarrow AB = 15km $<\/span><\/span><\/strong><\/p>\u0110a\u0301p a\u0301n \u0111u\u0301ng: C. 15 km.<\/span><\/strong><\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"147","test":"0","date":"2022-08-20 07:55:35","option_type":"txt","len":1},{"id":"9379","post_id":"5996","mon_id":"1158739","chapter_id":"1158740","question":"Ba\u0323n Ha\u0300 \u0111i xe \u0111a\u0323p t\u01b0\u0300 nha\u0300 t\u01a1\u0301i nha\u0300 sa\u0301ch ADC book, trong n\u1eeda quãng \u0111\u01b0\u1eddng \u0111\u1ea7u ba\u0323n Ha\u0300 \u0111i v\u1edbi tô\u0301c \u0111ô\u0323 20 km\/h. Tính tô\u0301c \u0111ô\u0323 c\u1ee7a ba\u0323n Ha\u0300 \u0111i trong n\u1eeda \u0111o\u1ea1n \u0111\u01b0\u1eddng còn l\u1ea1i. Bi\u1ebft r\u1eb1ng tô\u0301c \u0111ô\u0323 trung bình trong c\u1ea3 \u0111o\u1ea1n \u0111\u01b0\u1eddng là 23 km\/h.<\/p>","options":["A. 27,06 km\/h.","B. 32 km\/h.","C. 21,33 km\/h.","D. 26,07 km\/h."],"correct":"1","level":"3","hint":"S\u01b0\u0309 du\u0323ng ca\u0301c công th\u01b0\u0301c: $t = \\frac{s}{v}$<\/span> ; $Vtb = \\frac{s1+s2}{t1+t2}$<\/span><\/p>","answer":"Gia\u0309 s\u01b0\u0309 qua\u0303ng \u0111\u01b0\u01a1\u0300ng ba\u0323n Ha\u0300 \u0111i la\u0300 S. N\u01b0\u0309a qua\u0303ng \u0111\u01b0\u01a1\u0300ng la\u0300  $\\frac{S}{2}$<\/span><\/p>Go\u0323i tô\u0301c \u0111ô\u0323 c\u1ee7a ba\u0323n Ha\u0300 \u0111i trong n\u1eeda \u0111o\u1ea1n \u0111\u01b0\u1eddng còn l\u1ea1i la\u0300 $v_2$<\/span> (km\/h) Th\u01a1\u0300i gian ba\u0323n Ha\u0300 \u0111i trong n\u01b0\u0309a qua\u0303ng \u0111\u01b0\u01a1\u0300ng \u0111â\u0300u la\u0300  $t_1 = \\frac{s1}{v1} = \u200b\u200b\\frac{S}{2.20} = \\frac{S}{40} (h)$<\/span> Th\u01a1\u0300i gian ba\u0323n Ha\u0300 \u0111i trong n\u01b0\u0309a qua\u0303ng \u0111\u01b0\u01a1\u0300ng co\u0300n la\u0323i la\u0300  $t_2 = \\frac{s_2}{v_2} = \u200b\u200b\\frac{S}{2.v_2} (h)$<\/span> Ma\u0300 tô\u0301c \u0111ô\u0323 trung bình trong c\u1ea3 \u0111o\u1ea1n \u0111\u01b0\u1eddng là 23 km\/h nên  $V_{tb} = \\frac{s_1+s_2}{t_1+t_2} = {{\\frac{S}{2} + \\frac{S}{2}}\\over{\\frac{S}{40} +\\frac{S}{2.v_2}}} = 23$<\/span>  $\\Rightarrow {S\\over{S(\\frac{1}{40} + \\frac{1}{2.v_2})}} = 23 \\Rightarrow1 = 23.(\\frac{1}{40} + \\frac{1}{2.v_2})$<\/span>  $\\Rightarrow17.v_2 = 23.20 \\Rightarrow v_2\\approx 27,06km\/h$<\/span><\/span><\/strong><\/p>\u0110a\u0301p a\u0301n \u0111u\u0301ng: A. 27,06 km\/h.<\/span><\/strong><\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"147","test":"0","date":"2022-08-20 08:12:24","option_type":"txt","len":1},{"id":"9380","post_id":"5996","mon_id":"1158739","chapter_id":"1158740","question":"Buô\u0309i sa\u0301ng, cô Hoa b\u0103\u0301t \u0111â\u0300u \u0111i la\u0300m t\u01b0\u0300 7 h 00 min t\u01a1\u0301i n\u01a1i la\u0300m viê\u0323c la\u0300 7 h 30 min. Biê\u0301t tô\u0301c \u0111ô\u0323 trung bi\u0300nh cô \u0111i la\u0300 40 km\/h. Ho\u0309i qua\u0303ng \u0111\u01b0\u01a1\u0300ng t\u01b0\u0300 nha\u0300 t\u01a1\u0301i n\u01a1i la\u0300m viê\u0323c cu\u0309a cô Hoa la\u0300 bao nhiêu?<\/p>","options":["A. 40 km.","B. 20 km. \n ","C. 30 km.","D. 35 km."],"correct":"2","level":"3","hint":"S\u01b0\u0309 du\u0323ng công th\u01b0\u0301c: s = v.t<\/p>","answer":"Th\u01a1\u0300i gian \u0111i cu\u0309a cô Hoa la\u0300 7 h 30 min - 7 h 00 min = 30 min = 0,5 h Qua\u0303ng \u0111\u01b0\u01a1\u0300ng t\u01b0\u0300 nha\u0300 t\u01a1\u0301i n\u01a1i la\u0300m viê\u0323c cu\u0309a cô Hoa la\u0300 S = v . t = 40 . 0,5 = 20 km \u0110a\u0301p a\u0301n \u0111u\u0301ng: B. 20 km.<\/span><\/strong><\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"147","test":"0","date":"2022-08-20 08:16:50","option_type":"txt","len":1}]}