Cơ năng (trung bình)

Home Lớp 9 Khoa học tự nhiên 9 - sách kết nối tri thức Bài 3: Cơ năngBài tập trung bình

{"common":{"save":0,"post_id":"8303","level":2,"total":10,"point":10,"point_extra":0},"segment":[{"id":"9577","post_id":"8303","mon_id":"1159533","chapter_id":"1159535","question":"M\u1ed9t v\u1eadt có \u0111\u1ed9ng n\u0103ng t\u0103ng d\u1ea7n khi:<\/p>","options":["A. V\u1eadt \u0111\u01b0\u1ee3c nâng lên cao h\u01a1n.","B. V\u1eadt ch\u1ecbu tác d\u1ee5ng c\u1ee7a m\u1ed9t l\u1ef1c làm t\u0103ng v\u1eadn t\u1ed1c.","C. Th\u1ebf n\u0103ng c\u1ee7a v\u1eadt gi\u1ea3m d\u1ea7n. \n ","D. V\u1eadt di chuy\u1ec3n xu\u1ed1ng m\u1ed9t m\u1eb7t ph\u1eb3ng nghiêng mà không có ma sát. "],"correct":"2","level":"2","hint":"","answer":"\u0110áp án: B. V\u1eadt ch\u1ecbu tác d\u1ee5ng c\u1ee7a m\u1ed9t l\u1ef1c làm t\u0103ng v\u1eadn t\u1ed1c.<\/p>Gi\u1ea3i thích:<\/p>\u0110\u1ed9ng n\u0103ng ph\u1ee5 thu\u1ed9c vào v\u1eadn t\u1ed1c ($W_\u0111 = {1 \\over 2}mv^2$<\/span>). Khi có l\u1ef1c tác d\u1ee5ng làm t\u0103ng v\u1eadn t\u1ed1c, \u0111\u1ed9ng n\u0103ng c\u1ee7a v\u1eadt c\u0169ng t\u0103ng theo.<\/p>Xét các \u0111áp án:<\/p>A. Sai: Nâng v\u1eadt lên cao ch\u1ee7 y\u1ebfu làm th\u1ebf n\u0103ng t\u0103ng, ch\u01b0a ch\u1eafc \u0111\u1ed9ng n\u0103ng t\u0103ng. B. \u2705 \u0110úng: V\u1eadn t\u1ed1c t\u0103ng → \u0111\u1ed9ng n\u0103ng t\u0103ng. C. Ch\u01b0a ch\u1eafc: Th\u1ebf n\u0103ng gi\u1ea3m không nh\u1ea5t thi\u1ebft toàn b\u1ed9 chuy\u1ec3n thành \u0111\u1ed9ng n\u0103ng, vì có th\u1ec3 có ma sát ho\u1eb7c l\u1ef1c c\u1ea3n. D. \u0110úng trong tr\u01b0\u1eddng h\u1ee3p c\u1ee5 th\u1ec3: Tr\u01b0\u1ee3t xu\u1ed1ng m\u1eb7t ph\u1eb3ng nghiêng không ma sát → th\u1ebf n\u0103ng chuy\u1ec3n thành \u0111\u1ed9ng n\u0103ng → v\u1eadn t\u1ed1c và \u0111\u1ed9ng n\u0103ng t\u0103ng.<\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"125","test":"0","date":"2025-01-02 18:48:37","option_type":"txt","len":3},{"id":"9578","post_id":"8303","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 = 10 m. \u1ede \u0111\u1ed9 cao h = 5 m, c\u01a1 n\u0103ng c\u1ee7a v\u1eadt s\u1ebd:<\/p>","options":["A. B\u1eb1ng th\u1ebf n\u0103ng c\u1ee7a v\u1eadt \u1edf \u0111\u1ed9 cao ban \u0111\u1ea7u.","B. Gi\u1ea3m m\u1ed9t n\u1eeda so v\u1edbi c\u01a1 n\u0103ng ban \u0111\u1ea7u.","C. Không \u0111\u1ed5i so v\u1edbi c\u01a1 n\u0103ng ban \u0111\u1ea7u.","D. B\u1eb1ng \u0111\u1ed9ng n\u0103ng c\u1ee7a v\u1eadt t\u1ea1i \u0111\u1ed9 cao h = 5 m."],"correct":"3","level":"2","hint":"","answer":"\u0110áp án: C. Không \u0111\u1ed5i so v\u1edbi c\u01a1 n\u0103ng ban \u0111\u1ea7u.<\/p>Gi\u1ea3i thích:<\/p>Trong h\u1ec7 kín, không có ma sát, c\u01a1 n\u0103ng b\u1ea3o toàn:<\/p>$W = W_\u0111+ W_t$<\/span> (không \u0111\u1ed5i)<\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"125","test":"0","date":"2025-01-02 18:51:35","option_type":"txt","len":2},{"id":"9579","post_id":"8303","mon_id":"1159533","chapter_id":"1159535","question":"M\u1ed9t v\u1eadt \u0111ang chuy\u1ec3n \u0111\u1ed9ng trên m\u1eb7t \u0111\u1ea5t ph\u1eb3ng. Khi v\u1eadt d\u1eebng l\u1ea1i do ma sát, c\u01a1 n\u0103ng c\u1ee7a v\u1eadt \u0111ã:<\/p>","options":["A. Chuy\u1ec3n hóa hoàn toàn thành nhi\u1ec7t n\u0103ng.","B. Gi\u1ea3m m\u1ed9t n\u1eeda so v\u1edbi ban \u0111\u1ea7u.","C. T\u0103ng thêm vì v\u1eadt ch\u1ecbu tác d\u1ee5ng c\u1ee7a ma sát.","D. Không thay \u0111\u1ed5i vì c\u01a1 n\u0103ng luôn \u0111\u01b0\u1ee3c b\u1ea3o toàn."],"correct":"1","level":"2","hint":"","answer":"\u0110áp án: A. Chuy\u1ec3n hóa hoàn toàn thành nhi\u1ec7t n\u0103ng.<\/p>Gi\u1ea3i thích:<\/p>Khi v\u1eadt d\u1eebng l\u1ea1i, \u0111\u1ed9ng n\u0103ng ban \u0111\u1ea7u b\u1ecb tiêu hao do l\u1ef1c ma sát, chuy\u1ec3n hóa thành nhi\u1ec7t n\u0103ng, làm nóng b\u1ec1 m\u1eb7t ti\u1ebfp xúc.<\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"125","test":"0","date":"2025-01-02 21:11:22","option_type":"txt","len":3}]}