In a heat engine, if 500 J of heat enters the system, and the piston does 300 J of work. What is the final internal (thermal) energy of the system if the initial energy is 1,500 J?

200 J

800 J

1,300 J

1,700 J

The final answer is 1,700 J

Explanation: According to first law of thermodynamics:

=Final energy-initial energy=Change in internal energy

q = heat absorbed or released

w = work done by or on the system

w = work done by the system=  {Work done by the system is negative as the final volume is greater than initial volume}

q = +500J   {Heat absorbed by the system is positive}

w = work done by the system = -300J

U2- 1500J= + 500J --300J

U2= 1700J

1)H=714 Watts of energy is given out.

2)614.34 KCal energy is burnt in an hour in the room

3)In freezing conditions, 1337.09 KCal is spent in an hour.

Explanation:

The formula for thermal conductivity states that the rate of heat loss H is as follows:

H=   where,

K=Coefficient of thermal conductivity

A=Area of Cross Section

H=Rate of heat loss

x=Thickness of the material

=Temperature difference between the two surfaces of the body in context

=37°C ie. Body Temperature

=20°C ie. Room Temperature

For first case, =17°C or 17°F

K for fat= 0.21

A=2

x=0.01 m

H=

H=714 Watts of energy is given out.

2) ×

Energy= 714 × 60 × 60=2570400 J

2570400 J=614.3403442 KCal

Therefore, 614.3403442 KCal energy is burnt in an hour.

3) Only the temperature difference becomes 37°C from 17°C , rest everything remains the same, therefore the energy will also vary due to the temperature factor and more energy will be spent as in freezing climate °C

E==1337.09 KCal

In freezing conditions, 1337.09 KCal is spent in an hour.