Động năng. Thế năng (nâng cao)

Home Lớp 9 Khoa học tự nhiên 9 - sách kết nối tri thức Bài 2: Động năng. Thế năngBài tập nâng cao

{"common":{"save":0,"post_id":"8251","level":3,"total":10,"point":10,"point_extra":0},"segment":[{"id":"9587","post_id":"8251","mon_id":"1159533","chapter_id":"1159535","question":"M\u1ed9t v\u1eadt có kh\u1ed1i l\u01b0\u1ee3ng m = 2 kg r\u01a1i t\u1ef1 do t\u1eeb \u0111\u1ed9 cao h = 20 m. Tính v\u1eadn t\u1ed1c c\u1ee7a v\u1eadt khi ch\u1ea1m \u0111\u1ea5t (b\u1ecf qua l\u1ef1c c\u1ea3n không khí).<\/p>","options":["A. 10 m\/s","B. 15 m\/s","C. 20 m\/s","D. 25 m\/s"],"correct":"3","level":"3","hint":"","answer":"\u0110áp án: C. 20 m\/s<\/p>Gi\u1ea3i thích:<\/p>- C\u01a1 n\u0103ng \u0111\u01b0\u1ee3c b\u1ea3o toàn: $W_\u0111 = W_t$<\/span><\/p>Th\u1ebf n\u0103ng ban \u0111\u1ea7u: $W_t = mg = 2.10.20=400\\ J$<\/span><\/p>- Khi ch\u1ea1m \u0111\u1ea5t, toàn b\u1ed9 th\u1ebf n\u0103ng chuy\u1ec3n thành \u0111\u1ed9ng n\u0103ng: $W_\u0111 = {1 \\over 2}mv^2 <=> 400 ={1 \\over 2}.2.v^2 \\n$<\/span><\/p>$=> v = 20\\ m\/s$<\/span><\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"125","test":"0","date":"2025-01-05 20:23:49","option_type":"txt","len":0},{"id":"9588","post_id":"8251","mon_id":"1159533","chapter_id":"1159535","question":"M\u1ed9t lò xo có \u0111\u1ed9 c\u1ee9ng k = 200 N\/m b\u1ecb nén x = 0,1 m. Khi lò xo \u0111\u01b0\u1ee3c th\u1ea3 ra, v\u1eadn t\u1ed1c c\u1ef1c \u0111\u1ea1i c\u1ee7a m\u1ed9t v\u1eadt có kh\u1ed1i l\u01b0\u1ee3ng m = 2 kg g\u1eafn vào lò xo là:<\/p>","options":["A. 1 m\/s","B. 2 m\/s","C. 3 m\/s","D. 4 m\/s"],"correct":"1","level":"3","hint":"","answer":"\u0110áp án: A. 1 m\/s<\/p>Gi\u1ea3i thích:<\/p>- Th\u1ebf n\u0103ng \u0111àn h\u1ed3i ban \u0111\u1ea7u: $W_t= {1\\over 2}kx^2= {1\\over 2}.200.(0,1)^2= 1\\ J$<\/span><\/p>- Khi lò xo giãn h\u1ebft, toàn b\u1ed9 th\u1ebf n\u0103ng chuy\u1ec3n thành \u0111\u1ed9ng n\u0103ng: $W_\u0111 = {1 \\over 2}mv^2 <=> 1 = {1 \\over 2}.2.v^2$<\/span><\/p>=> v = 1 m\/s<\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"125","test":"0","date":"2025-01-05 20:29:57","option_type":"txt","len":0},{"id":"9589","post_id":"8251","mon_id":"1159533","chapter_id":"1159535","question":"M\u1ed9t v\u1eadt có kh\u1ed1i l\u01b0\u1ee3ng m = 3 kg \u0111ang \u1edf \u0111\u1ed9 cao h = 5. V\u1eadt r\u01a1i xu\u1ed1ng \u1edf \u0111\u1ed9 cao h' = 2 m. Tính v\u1eadn t\u1ed1c c\u1ee7a v\u1eadt t\u1ea1i \u0111\u1ed9 cao h'.<\/p>","options":["A. 5,4 m\/s","B. 6 m\/s","C. 7,7 m\/s","D. 8 m\/s"],"correct":"3","level":"3","hint":"","answer":"\u0110áp án: C. 7,7 m\/s<\/p>Gi\u1ea3i thích:<\/p>- Th\u1ebf n\u0103ng t\u1ea1i h = 5 m: $W_t = mgh= 3.10.5=150\\ J$<\/span><\/p>- Th\u1ebf n\u0103ng t\u1ea1i h' = 2 m: $W_t’=mgh’=3.10.2=60\\ J$<\/span><\/p>- Ph\u1ea7n th\u1ebf n\u0103ng chuy\u1ec3n thành \u0111\u1ed9ng n\u0103ng: $W_\u0111=W_t - W_t’=150-60=90\\ J$<\/span><\/p>- \u0110\u1ed9ng n\u0103ng: $W_\u0111 = {1 \\over 2}mv^2 => 90={1 \\over 2}.3.v^2$<\/span><\/p>=> $v = 7,7\\ m\/s$<\/span><\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"125","test":"0","date":"2025-01-05 22:04:46","option_type":"txt","len":0}]}