S gio dc v o to qung ninh -----------------------

k thi chn hc sinh gii cp tnh lp 12 THPT nm hc 2012-2013

Mn : VT L, BNG B

Thi gian lm bi : 180 pht (khng k thi gian giao )

Ngy thi : 23/10/2012 ( thi ny c 01 trang)

Cu 1: (4,5 im). Con lc n ca mt ng h gm si dy mnh khi lng khng ng k, vt nng lm bng cht c khi lng ring D = 8g/cm3. Khi dao ng nh trong bnh chn khng th ng h chy ng vi chu k dao ng l 2s. Cho con lc n dao ng nh trong bnh cha mt cht kh th thy chu k tng mt lng 0,00025s. Bit rng nhit v gia tc trng trng khng i, gi thit l cht kh ch c tc dng lc y Acsimt ln con lc n. 1. Tnh thi gian chy sai ca ng h trong mt ngy m. 2. Tnh khi lng ring ca cht kh . Cu 2: (3,5 im). Ngi ta dng bm bm mt ci sm xe p c th tch V = 2 lt. Sau khi bm, mt ngi i xe p ni trn thy din tch tip xc ca mi bnh xe vi mt ng l 20cm2. Khi lng ca ngi v xe l 80kg phn b u trn 2 bnh xe. Tnh thi gian bm mi bnh xe.

Bit rng ban u trong sm cha khng kh p sut p0 = 105Pa, coi nhit v th tch

sm khng i trong qu trnh bm. Xi lanh ca bm c chiu cao h = 0,5m v ng knh 5cm; thi gian mi ln bm l t0 = 4s; b qua th tch ca vi bm. Cu 3: (4,5 im). Trn b mt ca mt cht lng c hai ngun kt hp pht sng c 1S v 2S

cch nhau 8cm dao ng theo phng thng ng vi phng trnh u1 = u2 = acos200t. Vn tc truyn sng trn mt cht lng v = 0,8m/s. Bit im M mt cht lng nm trn ng trung trc ca on thng S1S2 v cch 1S khong d = 8cm. Coi bin sng khng i trong qu

trnh truyn sng. 1. Vit phng trnh sng tng hp ti im M. 2. Tm trn ng trung trc ca 1S 2S ni trn hai im gn M nht v dao ng cng

pha vi M. Cu 4: (4 im). t mt im sng A trn trc chnh v nm trc ca mt thu knh hi t.

Pha sau thu knh t mt mn chn E vung gc trc chnh ca thu knh. Mn E cch A mt on khng i a = 64cm. Khi tnh tin thu knh theo trc chnh t A ti mn E, ta thy vt sng trn mn khng bao gi thu li thnh mt im v khi thu knh cch mn E l b = 24cm

th bn knh vt sng trn mn c gi tr nh nht. Tnh tiu c ca thu knh. Cu 5: (3,5 im). Cho cc dng c sau: Mt ngun in mt chiu, mt vn k v mt ampe k khng l tng, mt bin tr v cc dy ni. Trnh by cch xc nh sut in ng v in tr trong ca ngun in. Ch : Khng c mc trc tip hai u ampe k vo hai cc ngun in phng trng hp dng qu ln lm hng ampe k.

.............................. Ht ................................

H v tn th sinh.S bo danh..

H v tn, ch k ca

gim th s 1: chnh thc