1. Shahjahan brain teaserproblems 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:-

2. (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:-

3. (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 theamount of heat given to a systembe 35j & amount of work doneby the systembe -15j,then
change in internal energy of systemis
(a)-50j (b)-20j (c)30j (d)50j
15.during theadiabatic expansion of 2 moles of a gas,thechange in internal energy was found to be
-100j. thework done during the process was:-
(a)zero (b)-100j (c)200j (d)100j
16.when a monoatomic gas expands at constantpressure, 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 raisethe temperature of 2 moles of an ideal gas at constant
pressurefrom30C to 35C. the amount of heat required in calories to raise the temperature of the
same gas through the samerange (30Cto 35C) at constant volume is:-
(a)30 (b)50 (c)70 (d)90
18.themaximum possible efficiency of an engine that absorbs heatat 327Cand 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 froma freezer at -23Cto the surroundingsat27C. it
coefficient of performanceis:-
(a)2.5 (b)5 (c)7.5 (d)10

4. 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