4 Piv txwv ntawm Cov Teeb Meem Kev Sib Txuas Nruj ntawm Cov Kua
1. Ib feem ntawm cov yeeb nkab muaj txoj kab uas hla 20 cm thiab lwm feem muaj txoj kab uas hla 10 cm. Yog tias qhov dej ntws ceev hauv qhov loj dua ntawm cov yeeb nkab yog 30 cm/s, ces qhov dej ntws ceev hauv qhov me dua ntawm cov yeeb nkab yog...
A. 80 cm/s
B. 100 cm/s
C. 120 cm/s
D. 130 cm/s
E. 140 cm/s
Kev Sib Tham:
Nws yog paub :
r1 = 10 cm, r2 Luas = 5 cm
v1 = 30 cm/s
Nug :
v2 ?
Jawb :
Kev sib txuas ntawm cov kua dej:
A1 v1 =A2 v2
Cov Ntaub Ntawv:
A1 = thaj tsam hla ntawm cov yeeb nkab 1, v1 = tus nqi dej ntws hauv cov yeeb nkab 1
A2 = thaj tsam hla ntawm cov yeeb nkab 2, v2 = tus nqi dej ntws hauv cov yeeb nkab 2
Thaj tsam ntawm cov yeeb nkab hla:
A1 = phi r12 = (3,14)(10 cm)2 = (3,14)(100 cm)2)
A2 = phi r22 = (3,14)(5 cm)2 = (3,14)(25 cm)2)
Tus nqi dej ntws hauv cov yeeb nkab 2:
A1 v1 =A2 v2
(3,14)(100 cm)2)(30 cm/s) = (3,14)(25 cm)2)(v2)
(100)(30 cm/s) = (25)(v)2)
3000 / 25 = v2
v2 = 120 cm/s
Cov lus teb yog C.
2. Roj ntws los ntawm cov yeeb nkab A mus rau cov yeeb nkab B thiab tom qab ntawd mus rau cov yeeb nkab C. Qhov piv ntawm thaj tsam ntawm cov yeeb nkab A thiab thaj tsam ntawm cov yeeb nkab C yog 5:3. Yog tias tus nqi ntws roj hauv cov yeeb nkab A sib npaug rau 2v, ces tus nqi roj ntws hauv cov yeeb nkab C yog ...
A. (3/10)v
B. 2v
C. (10/3)v
D. 5v
E. 9v
Kev Sib Tham:
Nws yog paub :
A1 = 5, Ib2 = 3, v1 = 2v
Nug :
v2 ?
Jawb :
A1 v1 =A2 v2
(5)(2v) = (3)(v)2)
10v = 3(v)2)
v2 = (10/3)v
Tus nqi roj ntws hauv cov yeeb nkab C yog (10/3)v
Cov lus teb yog C.
3. Ib qho kua dej ntws los ntawm ib lub yeeb nkab raws li qhia hauv daim duab hauv qab no. Yog tias thaj tsam hla A1 Luas = 8 cm2, A2 Luas = 2 cm2 thiab tus nqi ntawm cov kua v2 = 2 m/s ces qhov loj ntawm v1 yog ...
A. 0,5 ms-1
B. 1,0 ms-1
C. 1,5 ms-1
D. 2,0 ms-1
E. 2,5 ms-1
Kev Sib Tham
Nws yog paub :
Thaj tsam hla ntu 1 (A1) = 8 cm2
Thaj tsam hla ntu 2 (A2) = 2 cm2
Qhov ceev ntawm cov kua dej ntawm qhov hla ntu 2 (v2) = 2 m/s
Nug : qhov ceev ntawm cov kua ntawm qhov hla ntu 1 (v1)
Jawb :
Kev sib txuas ntawm cov kua dej :
A1 v1 =A2 v2
8 v1 = (2)(2)
8 v1 = 4
v1 = 4 / 8 = 0,5 m/s
Cov lus teb yog lawm yog A.
4. Saib daim duab! Yog tias txoj kab uas hla ntawm qhov loj yog ob npaug ntawm txoj kab uas hla ntawm qhov me, qhov ceev ntawm cov kua dej ntws hauv cov yeeb nkab me yog ...
A. 01 ms-1
B. 04 ms-1
C. 08 ms-1
D. 16 ms-1
E. 20 ms-1
Kev Sib Tham
Nws yog paub :
Txoj kab uas hla loj (d)1= 2 TZS
Lub vojvoog loj ntawm qhov hla (r)1) = ½ hnub1 = ½ (2) = 1
Thaj chaw loj ntawm qhov txiav (A1) = πr12 = π (1)2 = π (1)= π
Txoj kab uas hla me me (d)2= 1 TZS
Lub vojvoog me me ntawm qhov hla (r)2) = ½ hnub2 = ½ (1) = ½
Thaj chaw me me ntawm qhov txiav (A2) = πr22 = π (1/2)2 = π (1/4)= ¼ π
Qhov ceev ntawm cov kua dej ntws hauv qhov seem loj (v1) = 4 m/s
Nug : qhov ceev ntawm cov kua dej ntws ntawm qhov me me ntawm qhov seem v2)
Jawb :
Kev sib txuas ntawm cov kua dej :
A1 v1 =A2 v2
π 4 = ¼ π (v2)
4 = ¼ (v)2)
v2 = 8 m/s
Cov lus teb yog C.
