PHNG GD&T LNG SNTRNG THCS CAO DNG

KIM TRA HC K IINM HC 2014 - 2015

MN: VT L 8Thi gian lm bi 45pht (khng k thi gian giao )

Cu 1: (1,5 im)Vit cng thc tnh cng sut? Gii thch v nu n v cc i lng c

mt trong cng thc?Cu 2: (1,5 im)

Nu 3 nguyn l truyn nhit gia hai vt?Cu 3: (2,5 im)

Mt ng nghim ng y nc, t nng ming ng, gia hay yng th tt c nc trong ng u nng ln? Ti sao?Cu 4: (1 im)

Ni nhit dung ring ca nc l 4.200 J/kg.K iu c ngha l g?.Cu 5: (3,5 im)

Mt xoong nc bng ng c khi lng 1kg cha 3 lt nc 200C. Munun si xoong nc ny cn mt nhit lng bng bao nhiu?

(Cho bit nhit dung ring ca ng l 380 (J/kg.k) ca nc l 4200(J/kg.K)

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PHNG GD&T LNG SNTRNG THCS CAO DNG

HNG DN CHM KIM TRA HC K IINM HC 2014 - 2015

MN: VT L 8

Cu Hng dn chm im

1

Cng thc AP t 1,0

Trong : P - l cng sut, n v WA - l cng thc hin, n v J.t - l thi gian thc hin cng , n v s (giy). t l thi gian thc hin cng , n v s (giy).(

0,5

2

- Nhit t truyn t vt c nhit cao hn sang vt c nhit thp hn 0,5

- S truyn nhit xy ra cho ti khi nhit ca hai vt bng nhauth ngng li 0,5

- Nhit lng do vt ny ta ra bng nhit lng do vt kia thu vo 0,5

3t y ng 1,0V lp nc di i ln, cn lp nc trn i xung 0,5C nh th tt c nc trong ng u nng ln 1,0

4 C ngha l mun lm cho 1kg nc nng ln 10C cn truyn nhit

lng 4.200 J 1,0

5

Tm tt ngm1 = 1kgm2 = 3kgt1 = 200Ct2 = 1000CC1 = 380(J/kg.k)C2= 4200(J/kg.k)

Q = ?

0,5

+ Nhit lng cn cung cp cho m nc tng t 200C - 1000C l:ADCT: Q1 = m1.c2.(t2 - t1)

= 1.380.80 = 30400J1,0

+ Nhit lng cn cung cp cho nc tng t 200C - 1000C l:ADCT: Q2 = m2.c2.(t2 - t1)

= 3.4200.80 = 1008000J1,0

+ Nhit lng cn un si nc l:Q = Q1 + Q2

= 30400 + 1008000 = 1038400J = 1038,4 (kJ)1,0