3 cov lus nug txog kev sib npaug ntawm lub zog sib txhuam
1. Muab lub thaiv A hnyav 3 kg tso rau ntawm lub rooj thiab tom qab ntawd khi rau ntawm txoj hlua uas txuas nrog lub pob zeb B = 2 kg los ntawm lub pulley raws li qhia. Qhov hnyav thiab kev sib txhuam ntawm lub pulleys raug tsis quav ntsej. Kev nrawm vim yog lub ntiajteb txawj nqus g = 10 m/s2Txheeb xyuas qhov kev nrawm ntawm lub kaw lus thiab qhov nro hauv txoj hlua yog tias:
a) lub rooj du
b) cov lus qhia txog kev sib txhuam nrog tus coefficient ntawm kev sib txhuam kinetic ntawm 0.4
Paub:
Qhov hnyav ntawm thaiv A (mA) = 3 kg
Qhov hnyav ntawm pob zeb B (m)B) = 2 kg
Kev nrawm vim lub ntiajteb txawj nqus (g) = 10 m/s2
Qhov hnyav ntawm thaiv A (w)A) = mg = (3)(10) = 30 Newtons
Qhov hnyav ntawm pob zeb B (w)B) = mg = (2)(10) = 20 Newtons
SE pob: Qhov kev nrawm ntawm lub kaw lus (a) thiab qhov nro hauv txoj hlua (T)
tshuaj:
a) lub rooj du
Xam qhov kev nrawm ntawm lub system siv cov mis rau Newton txoj cai thib ob:
ΣF = ma
wB = (mA +mB) thiab
20 = (3 + 2) ib
20 = 5 ib
a = 20 / 5 = 4 m/s2
Xam qhov nro hauv txoj hlua siv cov mis rau qhov nro hauv txoj hlua:
Lub zog ntawm txoj hlua ntawm thaiv A:
ΣF = mA a
T = mA a = (3)(4) = 12 Newtons
Lub zog ntawm txoj hlua khi ntawm thaiv B:
ΣF = mB a
wB - T = (2)(4)
20 – T = 8
T = 20 – 8 = 12 Newtons
b) cov lus qhia txog kev sib txhuam nrog tus coefficient ntawm kev sib txhuam kinetic ntawm 0.4
Lub zog ntawm kev sib txhuam kinetic:
Fk = µk N = (0,4)(30) = 12 Newtons
Xam qhov kev nrawm ntawm lub system siv cov mis rau Newton txoj cai thib ob:
ΣF = ma
wB - fk = (mA +mB) thiab
20 – 12 = (3 + 2) ib
8 = 5 ib
a = 8 / 5 = 1,6 m/s2
Xam qhov nro hauv txoj hlua siv cov mis rau qhov nro hauv txoj hlua:
Lub zog ntawm txoj hlua ntawm thaiv A:
ΣF = mA a
T – fk = mA a
T – 12 = (3)(1,6)
T – 12 = 4,8
T = 4,8 + 12 = 16,8 Newtons
Lub zog ntawm txoj hlua khi ntawm thaiv B:
ΣF = mB a
wB - T = (2)(1,6)
20 – T = 3,2
T = 20 – 3,2 = 16,8 Newtons
2. Ib yam khoom uas muaj qhov hnyav 10 kg nyob hauv ib lub dav hlau kab rov tav. Tus coefficient ntawm kev sib txhuam zoo li qub yog 0.4 thiab tus coefficient ntawm kev sib txhuam kinetic yog 0.35. g = 10 m/s2Yog tias ib yam khoom muaj lub zog kab rov tav tas li ntawm 25 N, qhov loj ntawm lub zog sib txhuam uas ua rau yam khoom yog…
Paub:
Qhov hnyav ntawm yam khoom (m) = 10 kg
Tus coefficient ntawm kev sib txhuam Static (µ)s= 0.4 TZS
Tus coefficient ntawm kinetic friction (µk) = 0.35
Kev nrawm vim lub ntiajteb txawj nqus (g) = 10 m/s2
Lub zog kab rov tav (F) = 25 N
Lub zog nqus ntawm yam khoom (w) = mg = (10)(10) = 100 Newtons
Lub zog ib txwm (N) = w = 100 Newtons
SE pob: Qhov ntau ntawm kev sib txhuam static (f)s) thiab kinetic (fk)
tshuaj:
Lub zog ntawm kev sib txhuam static::
fs = µs N = (0,4)(100) = 40 Newtons
Lub zog ntawm Kinetic Friction:
fk = µk N = (0,35)(100) = 35 Newtons
Lub zog kab rov tav tsuas yog 25 Newtons xwb yog li nws tseem tsis tau txav cov khoom.
3. Qhov hnyav ntawm cov blocks A thiab B hauv daim duab yog 10 kg thiab 5 kg raws li. Tus coefficient ntawm kev sib txhuam ntawm block A thiab lub dav hlau yog 0.2. Yuav kom tiv thaiv block A kom tsis txhob txav mus los, qhov hnyav tsawg kawg nkaus ntawm block C xav tau yog…
Paub:
Qhov hnyav ntawm thaiv A (mA) = 10 kg
Qhov hnyav ntawm thaiv B (mB) = 5 kg
Coefficient ntawm kev sib txhuam zoo li qub ntawm thaiv A (µs= 0,2 TZS
Kev nrawm ntawm lub ntiajteb txawj nqus (g) = 10 m/s2
Qhov hnyav ntawm lub thaiv A (w)A) = mA g = (10)(10) = 100 Newtons
Qhov hnyav ntawm lub thaiv B (w)B) = mB g = (5)(10) = 50 Newtons
Kev sib txhuam zoo li qub (f)s) = µs N = (0,2)(w)A + wC) = (0,2)(100 + wC) = 20 + 0,2 wC
Nug: Qhov hnyav ntawm thaiv C kom lub cev so
Lus teb:
Lub kaw lus no nyob twj ywm yog li cov qauv rau Newton txoj cai thawj zaug siv:
ΣF = 0
wB - fs = 0
50 – (20 + 0,2 wC= 0 TZS
50 – 20 – 0,2 wC = 0
30 – 0,2 wC = 0
30 = 0,2 wC
wC = 30 / 0,2 = 300 / 2 = 150 Newtons
Qhov hnyav ntawm thaiv C = 150 / 10 = 15 Kg
