5 mau laʻana o nā pilikia wela
1. ʻO ka tini me ke kaumaha o 2 kilokani he wela kikoʻī ko 130 J.kg -1 C -1 . ʻO ka nui o ka wela i omo ʻia e ka tini e hoʻokiʻekiʻe i kona mahana mai 50 o C a i 100 o C ʻo….
Pahana
Ua ʻike ʻia:
Nuipaʻa (m) = 2 kg
Ka wela kikoʻī o ka tin (c) = 130 J.kg -1 C -1
Ka loli ʻana o ka mahana (Δ T) = 100 o C – 50 o C = 50 o C
Nīnau: Ka wela (Q) i omo ʻia e ka tini
Pane:
Haʻilula wela:
Q = mcΔT
Wehewehe: Q = wela, m = nuipa, c = wela kikoʻī, Δ T = loli o ka mahana
Ka wela i omo ʻia e ka tin:
Q = (2 kg)(130 J.kg -1 C -1 )(50 o C)
Q = (100)(130)
Q = 13000 Joule
Q = 1,3 x 10 4 Joule
2. ʻO ke keleawe me ka wela kikoʻī o 390 J kg -1 o C -1 e ʻike i kahi loli mahana o 40 o C. Inā ʻo ka wela i omo ʻia e ke keleawe i ka wā o ka loli mahana he 200 calories, a laila ʻo ke kaumaha o ke keleawe he...
Pahana
Ua ʻike ʻia:
Ka wela kikoʻī o ke keleawe (c) = 390 J kg -1 o C -1
Ka loli ʻana o ka mahana (ΔT ) = 40 o C
Ka wela (Q) = 40 Joules
Nīnau: Nuipaʻa (m) o ke keleawe
Pane:
Q = mcΔT
40 = (m)( 390 )(40 ° C)
40 = (m)(390 )(40)
40 = (m)( 390 )(4)
40 = (m)( 1560 )
m = 40 / 1560
m = 0,026 kg
ʻO ke kaumaha o ke keleawe he 26 grams.
3. ʻO ka wai me ke kaumaha o 20 grams me ka wela kikoʻī o 1 cal g -1 o C -1 i ka wā mua he 30 o C ka mahana. E hoʻoholo i ka loli o ka mahana o ka wai inā he 300 calories ka nui o ka wela i omo ʻia e ka wai!
Pahana
Ua ʻike ʻia:
Nuipaʻa (m) = 20 gr
Mahana mua (T 1 ) = 30 o C
Ka wela kikoʻī o ka wai (c) = 1 cal gr -1 o C -1
Ka wela (Q) = 300 kal
Nīnau ʻia: Nā loli o ka mahana o ka wai
Pane:
Q = mcΔT
Q = mc (T 2 – T 1 )
300 kal = (20 gr)( 1 kal gr -1 o C -1 )(T 2 – 30 o C)
300 = (20)(1)(T 2 – 30)
300 = 20 (T 2 – 30)
300 = 20 T 2 – 600
300 + 600 = 20 T 2
900 = 20 T 2
T 2 = 900 / 20
T 2 = 45 o C
Nā loli o ka mahana:
Δ T = 45 o C – 30 o C
ΔT = 15 ° C
4. ʻO ka nui o ka wela e pono ai e hoʻohaʻahaʻa i ka mahana o 4 kg o ka wai nona ka wela kikoʻī o 500 J/kg K mai 40 oLilo ʻo C i 20 oʻO C…
A. 20 kJ
B. 30 kJ
C. 40 kJ
D. 50 kJ
E. 60 kJ
Kūkākūkā:
Ua ʻike ʻia :
Nuipaʻa (m) = 4 kg
Ka wela kikoʻī (c) = 500 J/kg K = 500 J/kg Co
Ka loli ʻana o ka mahana (delta T) = 40 oC - 20 oC = 20 Co
Ua nīnau ʻia :
Wela (Q)
Pane :
Formula Wela :
Q = (m)(c)(delta T)
Q = (4)(500)(20) = 40.000 Joules = 40 kJ
kJ = kilo Joule
ʻO C ka pane pololei.
5. Ua hoʻomehana ʻia kahi mea paʻa me ke kaumaha o 2 kg mai ka mahana o 30oLilo ʻo C i 100oC, koi i ka wela 7 × 105 Joule. ʻO ka wela kikoʻī o ka mea…
A. 400 J/kg K
B. 500 J/kg K
C. 700 J/kg K
D. 1000 J/kg K
E. 5000 J/kg K
Kūkākūkā:
Ua ʻike ʻia :
Nuipaʻa (m) = 2 kg
Wela (Q) = 7 × 105 J = 700.000 J
Ka loli ʻana o ka mahana (delta T) = 100 oC - 30 oC = 70 Co
Ua nīnau ʻia :
Ka wela kikoʻī (c) ?
Pane :
c = Q / mT
c = 700.000 J / (2 kg)(70 Co) = 700.000 J / 140 kg Co
c = 5000 J/kg Co
c = 5000 J/kg K
ʻO ka pane pololei ʻo E.
