Shahjahan brain teaser problems of physics on heat and thermodynamics

1.A lead bullet strikes armour plate with velocity of 300m/s and is completely stopped. If the heat produce is shared equally between the

bullet and the target,the rise in the temperature of the bullet is (the specific heat of lead is 0.03cal/gC):-

(a)89.3C (b)49.3C (c)178.6C (d)357.2C

2.The temperatures of equal masses of three different liquids A, B and C are 12C,19C and 28C respectively. When A and B are mixed the temperature is 16C and when B and C are mixed,it is 23C.the temperature when A and C mixed is

(a)10.1C (b)20.2C (c)30.3C (d) 40.4C

3.A perfect gas at 27C is heated at constant pressure so as to double its volume. The temperature of gas becomes:-

(a)54C (b)150K (c)327C (d)327K

4.Two identical cylinders contain He at 2.5atm and argon at 1atm. If both the gases are filled in one of the cylinders the pressure would be (in atmosphere):-

(a)1.75 (b)3.5 (c)4.75 (d)7.0

5.the temperature at the bottom of a 40m deep lake is 12C and that at the surface is 35C. an air bubble of volume 1.0cm’3 rises from the bottom to the surface. Its volume becomes (atmospheric pressure=10m of water):-

(a)2.0cm^3 (b)3.2cm^3 (c)5.4cm^3 (d)8.0cm^3

6.oxygen and hydrogen gases are at the same temperature. The ratio of the average kinetic energy of an oxygen molecule and that of a hydrogen molecule is:-

(a)16 (b)4 (c)1 (d)1/4

7.two gases are enclosed in a container at constant temperature. One of the gases,which is diatomic,has relative molecular mass eight times the other,which is monoatomic. The ratio of r.m.s speed of the molecules of the monoatomic gas to that of the molecules of the diatomic gas is:-

(a)8 (b)4 (c)2 (d)2

8.the 1.20kg head of a hammer has a speed of 8m/s. just before it strikes a nail and is brought to rest. estimate the temperature rise of a 14g iron nail generated by ten such hammer blows done in quick succession(assume the nail has absorb all the energy) the specific heat of lead is 450J/kg-c

(a)85C (b)99C (c)61C (d)70C

9.The pressure of a gas contained in a closed vessel is increased by 0.4% when heated by 1C. the initial temperature was:-

(a)250k (b)250C (c)500K (d)500C

10.two different ideal gases are enclosed in two different vessels at the same pressure. If P1 and P2 are their densities and V1 and V2 are their r.m.s speeds,respectively,then V1/ V2

is equal to:-

(a)p1^2/p2^2 (b)p2^2/p1^2 (c)(p1/p2)^1/2 (d)(p2/p1)^1/2

11.if intermolecular forces vanish the volume occupied by the molecules of 4.5kg water at S.T.P will be:-

(a)5.6m^3 (b)11.2litre (c)4.5m^3 (d)11.2m^3

12.four molecules have speeds 2km/s,3km/s,4km/s and 5km/s. the r.m.s speed of these molecules in km/s is:-

(a) (b) (c)3.5 (d)

13.the equation of state corrosponding to 8g of O2 is:-

(a)PV=8RT (b)PV=RT/4 (c)PV=RT (d)PV=RT/2

14.If the amount of heat given to a system be 35j & amount of work done by the system be -15j,then change in internal energy of system is

(a)-50j (b)-20j (c)30j (d)50j

15.during the adiabatic expansion of 2 moles of a gas,the change in internal energy was found to be

-100j. the work done during the process was:-

(a)zero (b)-100j (c)200j (d)100j

16.when a monoatomic gas expands at constant pressure, the percentage of heat supplied that increases the internal energy of the gas & that which is involved in expansion is:-

(a)75%,25% (b)25%,75% (c)60%,40% (d)40%,60%

17. 70 calories of heat are required to raise the temperature of 2 moles of an ideal gas at constant pressure from 30C to 35C. the amount of heat required in calories to raise the temperature of the same gas through the same range (30C to 35C) at constant volume is:-

(a)30 (b)50 (c)70 (d)90

18.the maximum possible efficiency of an engine that absorbs heat at 327C and exhaust heat at 127C is:-

(a)1/3 (b)1/2 (c)2/3 (d)1/4

19.an ideal refrigerator is used to transfer heat from a freezer at -23C to the surroundings at 27C. it coefficient of performance is:-

(a)2.5 (b)5 (c)7.5 (d)10

20.the temperature of source & sink in a carnot engine are 400k,and 300k respectively.if the engine receives 600cal of heat from source per cycl, the heat rejected to the sink per cycle is:-

(a)150cal (b)300cal (c)400cal (d)450cal

21.a carnot engine working, between 300k & 600k has a work output of 800j per cycle. The amount of heat energy supplied to the engine from source per cycle is:-

(a)1200j (b)2400j (c)1600j (d)3200j

22.the pressure and density of a diatomic gas (gama=7/5) change adiabatically from (P,p) to (P’,p’). if (P’/p’)=32 then (P’/P’) is:-

(a)128 (b)1/128 (c)32 (d)non of these

ANSWER SHEET

(1).c(2).b(3).c(4).b(5).c(6).c(7).c(8).c(9).a(10).d(11).a(12).b(13).b

(14).d(15).d(16).c

(17).b(18).a (19).b (20).d (21).c (22).a