{"id":610,"date":"2025-08-06T15:05:10","date_gmt":"2025-08-06T15:05:10","guid":{"rendered":"https:\/\/giapsgk.com\/chuyen-de\/?page_id=610"},"modified":"2025-08-06T15:05:10","modified_gmt":"2025-08-06T15:05:10","slug":"tim-x-v-a-tai-thoi-diem-t","status":"publish","type":"page","link":"https:\/\/giapsgk.com\/chuyen-de\/dao-dong\/dao-dong-dieu-hoa\/tim-x-v-a-tai-thoi-diem-t\/","title":{"rendered":"T\u00ecm x, v, a t\u1ea1i th\u1eddi \u0111i\u1ec3m t"},"content":{"rendered":"

V\u00ed d\u1ee5 1:<\/strong> M\u1ed9t ch\u1ea5t \u0111i\u1ec3m dao \u0111\u1ed9ng \u0111i\u1ec1u h\u00f2a c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh v\u1eadn t\u1ed1c l\u00e0 v = 4\u03c0cos(2\u03c0t) cm\/s. G\u1ed1c t\u1ecda \u0111\u1ed9 \u1edf v\u1ecb tr\u00ed c\u00e2n b\u1eb1ng. M\u1ed1c th\u1eddi gian \u0111\u01b0\u1ee3c ch\u1ecdn v\u00e0o l\u00fac ch\u1ea5t \u0111i\u1ec3m c\u00f3 li \u0111\u1ed9 v\u00e0 v\u1eadn t\u1ed1c l\u00e0<\/p>\n

A. x = 2 cm v\u00e0 v = 0.<\/p>\n

B. x = 0 v\u00e0 v = 4\u03c0 cm\/s.<\/p>\n

C. x = – 2 cm v\u00e0 v = 0.<\/p>\n

D. x = 0 v\u00e0 v = – 4\u03c0 cm\/s.<\/p>\n

Gi\u1ea3i<\/strong><\/p>\n

$\\left\\{ \\begin{array}{l} x = A\\cos \\left( {\\omega t + \\varphi } \\right)\\\\ v = – A\\omega \\sin \\left( {\\omega t + \\varphi } \\right) = A\\omega c{\\rm{os}}\\left( {\\omega t + \\varphi + \\frac{\\pi }{2}} \\right) \\end{array} \\right.$$ \\to \\left\\{ \\begin{array}{l} \\varphi = – \\frac{\\pi }{2}\\left( {rad} \\right)\\\\ A = 2cm \\end{array} \\right.$$ \\to \\left\\{ \\begin{array}{l} x = 2\\cos \\left( {2\\pi .0 – \\frac{\\pi }{2}} \\right) = 0\\\\ v = 4\\pi c{\\rm{os}}\\left( {2\\pi .0} \\right) = 4\\pi \\left( {\\frac{{cm}}{s}} \\right) \\end{array} \\right.$<\/p>\n

Ch\u1ecdn C.<\/p>\n

V\u00ed d\u1ee5 2:<\/strong> V\u1eadt dao \u0111\u1ed9ng \u0111i\u1ec1u h\u00f2a v\u1edbi ph\u01b0\u01a1ng tr\u00ecnh: x = 20cos(2\u03c0t – \u03c0\/12) (cm) (t \u0111o b\u1eb1ng gi\u00e2y). Gia t\u1ed1c c\u1ee7a v\u1eadt t\u1ea1i th\u1eddi \u0111i\u1ec3m t = 5\/24 (s) l\u00e0:<\/p>\n

A. 2 m\/s2.<\/p>\n

B. 9,8 m\/s2.<\/p>\n

C. – 4 m\/s2.<\/p>\n

D. 10 m\/s2.<\/p>\n

Gi\u1ea3i<\/strong><\/p>\n

$\\begin{array}{l} t = \\frac{5}{{24}}\\left( s \\right)\\\\ \\to x = 20\\cos \\left( {2\\pi .\\frac{5}{{24}} – \\frac{\\pi }{{12}}} \\right) = 10\\left( {cm} \\right)\\\\ \\to a = – {\\omega ^2}x = – 4\\left( {\\frac{m}{{{s^2}}}} \\right) \\end{array}$<\/p>\n

Ch\u1ecdn C.<\/p>\n

V\u00ed d\u1ee5 3<\/strong>: M\u1ed9t v\u1eadt dao \u0111\u1ed9ng \u0111i\u1ec1u h\u00f2a v\u1edbi ph\u01b0\u01a1ng tr\u00ecnh: x = 4cos(2\u03c0t – \u03c0\/3) (cm) (t \u0111o b\u1eb1ng gi\u00e2y). V\u00e0o th\u1eddi \u0111i\u1ec3m t = 2,5 s th\u00ec li \u0111\u1ed9 v\u00e0 v\u1eadn t\u1ed1c c\u1ee7a v\u1eadt b\u1eb1ng<\/p>\n

A. $x=2cm;\\,v=4\\pi \\sqrt{3}\\frac{cm}{s}.$<\/p>\n

B. $x=2cm;\\,v=-4\\pi \\sqrt{3}\\frac{cm}{s}.$<\/p>\n

C. $x=-2cm;\\,v=-4\\pi \\sqrt{3}\\frac{cm}{s}.$<\/p>\n

D. $x=-2cm;\\,v=4\\pi \\sqrt{3}\\frac{cm}{s}.$.<\/p>\n

Gi\u1ea3i<\/strong><\/p>\n

$\\left\\{ \\begin{array}{l} t = 2,5\\left( s \\right)\\\\ x = 4\\cos \\left( {2\\pi .t – \\frac{\\pi }{3}} \\right)\\\\ v = – 2\\pi .4\\sin \\left( {2\\pi .t – \\frac{\\pi }{3}} \\right) \\end{array} \\right.$ $ \\to \\left\\{ \\begin{array}{l} t = 2,5s\\\\ x = – 2cm\\\\ v = – 4\\pi \\sqrt 3 \\frac{{cm}}{s} \\end{array} \\right.$<\/p>\n

Ch\u1ecdn C.<\/p>\n

V\u00ed d\u1ee5 4:<\/strong> V\u1eadt dao \u0111\u1ed9ng \u0111i\u1ec1u h\u00f2a v\u1edbi ph\u01b0\u01a1ng tr\u00ecnh x = 4cos(20t + \u03c0\/3) ( v\u1edbi x t\u00ednh b\u1eb1ng cm v\u00e0 t t\u00ednh b\u1eb1ng gi\u00e2y). V\u00e0o th\u1eddi \u0111i\u1ec3m ban \u0111\u1ea7u v\u1eadn t\u1ed1c v\u00e0 gia t\u1ed1c c\u1ee7a v\u1eadt<\/p>\n

A. $a=-8\\left( \\frac{cm}{{{s}^{2}}} \\right);v=-40\\sqrt{3}\\left( \\frac{cm}{s} \\right).$<\/p>\n

B. $a=-8\\left( \\frac{m}{{{s}^{2}}} \\right);v=-40\\sqrt{3}\\left( \\frac{cm}{s} \\right).$<\/p>\n

C. $a=8\\left( \\frac{m}{{{s}^{2}}} \\right);v=40\\sqrt{3}\\left( \\frac{cm}{s} \\right).$<\/p>\n

D. $a=8\\left( \\frac{cm}{{{s}^{2}}} \\right);v=-40\\sqrt{3}\\left( \\frac{cm}{s} \\right).$.<\/p>\n

Gi\u1ea3i<\/strong><\/p>\n

$\\left\\{ \\begin{array}{l} x = 4\\cos \\left( {20t + \\frac{\\pi }{3}} \\right)cm\\\\ v = – 80\\sin \\left( {20t + \\frac{\\pi }{3}} \\right)\\left( {\\frac{{cm}}{s}} \\right)\\\\ a = – {\\omega ^2}x \\end{array} \\right.$<\/p>\n

Khi t = 0<\/p>\n

$\\left\\{ \\begin{array}{l} x = 4\\cos \\left( {20.0 + \\frac{\\pi }{3}} \\right) = 2cm \\to a = – 8\\left( {m\/{s^2}} \\right)\\\\ v = – 80\\sin \\left( {20.0 + \\frac{\\pi }{3}} \\right)\\left( {\\frac{{cm}}{s}} \\right) = – 40\\sqrt 3 \\left( {cm\/s} \\right) \\end{array} \\right.$<\/p>\n

Ch\u1ecdn B.<\/p>\n","protected":false},"excerpt":{"rendered":"

V\u00ed d\u1ee5 1: M\u1ed9t ch\u1ea5t \u0111i\u1ec3m dao \u0111\u1ed9ng \u0111i\u1ec1u h\u00f2a c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh v\u1eadn t\u1ed1c l\u00e0 v = 4\u03c0cos(2\u03c0t) cm\/s. G\u1ed1c t\u1ecda \u0111\u1ed9 \u1edf v\u1ecb tr\u00ed c\u00e2n b\u1eb1ng. M\u1ed1c th\u1eddi gian \u0111\u01b0\u1ee3c ch\u1ecdn v\u00e0o l\u00fac ch\u1ea5t \u0111i\u1ec3m c\u00f3 li \u0111\u1ed9 v\u00e0 v\u1eadn t\u1ed1c l\u00e0 A. x = 2 cm v\u00e0 v = 0. B. x … \u0110\u1ecdc ti\u1ebfp<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":580,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-610","page","type-page","status-publish"],"_links":{"self":[{"href":"https:\/\/giapsgk.com\/chuyen-de\/wp-json\/wp\/v2\/pages\/610","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/giapsgk.com\/chuyen-de\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/giapsgk.com\/chuyen-de\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/giapsgk.com\/chuyen-de\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/giapsgk.com\/chuyen-de\/wp-json\/wp\/v2\/comments?post=610"}],"version-history":[{"count":2,"href":"https:\/\/giapsgk.com\/chuyen-de\/wp-json\/wp\/v2\/pages\/610\/revisions"}],"predecessor-version":[{"id":618,"href":"https:\/\/giapsgk.com\/chuyen-de\/wp-json\/wp\/v2\/pages\/610\/revisions\/618"}],"up":[{"embeddable":true,"href":"https:\/\/giapsgk.com\/chuyen-de\/wp-json\/wp\/v2\/pages\/580"}],"wp:attachment":[{"href":"https:\/\/giapsgk.com\/chuyen-de\/wp-json\/wp\/v2\/media?parent=610"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}