Question

16) IN ORDER TO MAKE ICE CUBES (WHICH AREN'T REALLY CUBES), THE ICEMAKER IN A REFRIGERATOR LETS IN 290 GRAMS OF LIQUID WATER AT AN ORIGINAL TEMPERATURE OF 16°C, TURNS IT SOLID WATER AT OC, AND COOLS THE ICE TO -10°C. FOR EACH BATCH OF ICE , How MUCH THERMAL ENERGY MUST BE REMOVED ? ΤΟ (A) 25,000 J (B) 6 1,000 J (C) 97,000 J (D) 122,000 J 10 E(N) 4 + 20+ A NON - CONSTANT FORCE ACTS ON A 4.0 KG MASS FOR 18 SECONDS AS SHOWN AT LEFT. AT t=, THE VELOCITY OF THE MASS WAS Vo = = -7.0 m/s. At t= 18.5., THE VELOCITY WILL BE CLOSEST To : + lo O #t(s) o lo (A) +21 m/s (D) + 45 m/s (B) + 28 m/s (c) + 38 m/s CE) + 52 m/s 18) A LOG CABIN HAS WOOD WALLS 20 CM THICK. THE THERMAL CONDUCT TVITY OF WOOD is 0.15 ms.co. ONE WALLS 3.0m HIGH AND 5.8m WIDE. IF THE INSIDE TEMPERATURE IS 22°C AND THE OUTSIDE TEMPERATURE IS 8°C, HOW MUCH THERMAL ENERGY PASSES THROUGH THE WALL EACH SECOND ? (A) 563 B) 392 TS (C) 287 3 (D) 196 T/s 19) A MASS m = 0.250 KG HANGS IN EQUILBRIUM ON A SPRING SUSPENDED FROM A HOOK AS IN LAB #9. THE MASS IS THEN PULLED DOWN WARD A DISTANCE OF 18 CM AND RELEASED THE MASS EXECUTES SIMPLE HARMONIC MOTION VERTICALLY WITH A PERIOD OF 0.68 SECONDS THE ELASTIC CONSTANT FOR THE SPRING IS CLOSEST TO : (A) 7.8 N/m (B) 15 N/m (c) 21 N/m CD) 36 N/m

Answer 1

16)

m = mass of water = 290 g = 0.290 kg

Sw = specific heat of water = 4186 J/kg/K

L = latent heat of freezing = 333000 J/kg

Si = specific heat of ice = 2095 J/kg/K

initial temperature Ti = 16 degree celsius

final temperature Tf = - 10 degree celsius

Total thermal energy removed =

=

  $\approx 122000 J$ [correct option is D]

17)

the slope of graph is = 20/18 = 10/9

the variation of force with time is $F = \frac{10}{9}t$ .

assume initial velocity is u = 7 m/s left. = -7 m/s

and the force is towards right.

m = 4 kg

acceleration of body = a = F/m = $\bg_white \frac{10t}{9m} = \frac{10t}{9*4} =\frac{5t}{18}$ .

also, $a=\frac{dv}{dt}$

therefore,

$\frac{dv}{dt}=\frac{5t}{18}$

$\Rightarrow dv=\frac{5t}{18}*dt$

$\Rightarrow \int_{-7}^{v}dv=\int_{0}^{18}\frac{5t}{18}*dt$

=> v - (-7) = 45

=> v = 45 - 7 = +38 m/s [correct option is option C]