3 Cov Lus Nug Txog Kev Sib Npaug Ntawm Txoj Hlua
1. Daim duab hauv qab no qhia peb lub thaiv, uas yog A, B thiab C uas nyob rau ntawm ib lub dav hlau kab rov tav. Yog tias qhov hnyav A = 1 kg, qhov hnyav B = 2 kg thiab qhov hnyav C = 2 kg thiab F = 10 N, ces txiav txim siab qhov piv ntawm qhov kev nruj hauv txoj hlua ntawm A thiab B rau qhov kev nruj hauv txoj hlua ntawm B thiab C.
Paub:
Qhov hnyav ntawm A (mA ) = 1 kg
Qhov hnyav B (mB ) = 2 kg
Qhov hnyav ntawm C (mC ) = 2 kg
Lub zog tensile (F) = 10 N
Xav tau: T AB : T BC
tshuaj:
Xam qhov kev nrawm ntawm lub system siv Newton's Second Law formula:
ΣF = ma
F = (m A + m B + m C ) a
10 = (1 + 2 + 2) ib
10 = 5 ib
ib = 10 / 5
a = 2 m/s 2
Siv cov qauv ntawm txoj hlua los xam T AB
ΣF = ma
T AB = m A a = 1 (2) = 2 Newtons
Siv cov qauv ntawm txoj hlua los xam T BC
ΣF = ma
T BC = (m A + m B ) a = (1 + 2) (2) = (3)(2) = 6 Newtons
2. Khoom A uas hnyav 6 kg thiab khoom B uas hnyav 3 kg raug txuas los ntawm ib txoj hlua raws li qhia. Yog tias tus coefficient ntawm kev sib txhuam yog 0.3 thiab g = 10 m/s2 , txiav txim siab qhov kev nrawm ntawm khoom thiab qhov nro hauv cov hlua ntawm txhua lub thaiv.
Paub Tias:
Qhov hnyav ntawm yam khoom A (mA ) = 6 kg
Qhov hnyav ntawm yam khoom B (mB ) = 3 kg
Coefficient ntawm kev sib txhuam ntawm thaiv A (µk ) = 0.3
Kev nrawm vim lub ntiajteb txawj nqus (g) = 10 m/s 2
Qhov hnyav ntawm thaiv A (w A ) = m A g = (6)(10) = 60 N
Lub zog ib txwm muaj rau ntawm thaiv A (N A ) = w A = 60 N
Qhov hnyav ntawm thaiv B (w B ) = m B g = (3)(10) = 30 N
Xav tau: Qhov kev nrawm ntawm lub kaw lus (a) thiab qhov nro hauv txoj hlua (T)
tshuaj:
Xam lub zog kinetic frictional force piv txwv li lub zog frictional thaum thaiv A txav mus los:
F k = µ k N A = (0,3)(60) = 18 Newtons
Xam qhov kev nrawm ntawm lub kaw lus (a):
ΣF = ma
wB – Fk = (m A + m B ) a
30 – 18 = (6 + 3) ib
12 = 9 ib
a = 12 / 9 = 1,3 m/s 2
Xam qhov nro hauv txoj hlua ntawm thaiv A (TA ) :
ΣF = ma
TA – Fk = ( mA ) a
TA – 18 = (6)(1,3)
TA – 18 = 7,8
TA = 7,8 + 18 = 25,8 Newtons
Xam qhov nro ntawm txoj hlua ntawm lub beam B (Tb ) :
ΣF = ma
w B – TB = m B (a)
30 – TB = 3 (1,3)
30 – TB = 3,9
TB = 30 – 3,9
T₂ = 26,1 Newtons
3. Ob yam khoom A thiab B uas muaj qhov hnyav ntawm 5 kg thiab 3 kg raug txuas los ntawm lub pulley uas tsis muaj kev sib txhuam. Lub zog P raug siv rau lub pulley mus rau sab saud. Yog tias ob lub blocks pib so ntawm hauv pem teb, qhov kev nrawm ntawm lub block A yog dab tsi, yog tias qhov loj ntawm P yog 60 N?
Txheeb xyuas qhov nro ntawm txoj hlua ntawm cov blocks A thiab B.
Paub Tias:
Kev nrawm vim lub ntiajteb txawj nqus (g) = 10 m/s 2
Qhov hnyav ntawm A (mA ) = 5 kg
Qhov hnyav ntawm thaiv A (w A ) = m A g = (5)(10) = 50 Newtons
Qhov hnyav B (mB ) = 3 kg
Qhov hnyav ntawm thaiv B (w B ) = m B g = (3)(10) = 30 Newtons
Lub zog P = 60 N
Xav tau: Kev ua kom nrawm ntawm lub kaw lus ntawm cov nqaj A thiab B (a) thiab qhov nro hauv txoj hlua ntawm cov nqaj A (T A ) thiab cov nqaj B (T B )
tshuaj:
Xam qhov kev nrawm ntawm lub system siv Newton's Second Law formula.
ΣF = ma
w A – w B = (m A + m B ) a
50 – 30 = (5 + 3) ib
20 = 8 ib
ib = 20 / 8
a = 2,5 m/s 2
Siv cov qauv tension force los xam qhov tension hauv txoj hlua
Lub zog ntawm txoj hlua ntawm thaiv A:
ΣF = ma
w A – TA = m A a
50 – TA = 5 (2,5)
50 – TA = 12,5
TA = 50 – 12,5 = 37,5 Newtons
Lub zog ntawm txoj hlua khi ntawm thaiv B:
ΣF = ma
TB – wB = mB a
TB – 30 = 3 (2,5)
TB – 30 = 7,5
TB = 7,5 + 30 = 37,5 Newtons
