The U. S. Military provides personnel on deployment with fuel bars to heat up their meals. A fuel bar provides 380.0 kJ of energy, and 73% of that energy can be transferred to food. How many ounces of water could be heated by one fuel bar to brew coffee in the field? The initial temperature of the water is 16.0°C and it needs to be heated to boiling at 100.0°C.

Explanation:

380 x 10³ J

73% of 380 x 10³ = 277.4 x 10³ J

mass of water = m gram

heat used to boil water = m x 4.2 x ( 100 - 16 )

= 352.8 m = 277.4 x 10³

m = 786.3 g

1 gram = .0352 ounce

786.3 gram = 786.3 x  .0352 ounce

= 27.68 ounce .

first let us lay out the formula for potential

and kinetic energy:

pe = mgh

ke = (mv^2)/2

where: m=mass, v=velocity, g=gravitational

acceleration, h=height

calculating for mass using the known values of

pe:

340j = m (9.81 m/s^2) (50ft) (1m/3.28ft)

m = 2.27 kg

the law of conservation of energy states that

energy is neither created nor destroyed. therefore, the change in kinetic

energy from 50 ft to 35 ft would be equal to the change in potential energy

from 50 ft to 35 ft. however it would be opposite in signs since one is losing

while other is gaining.

ke(35ft) – ke(50ft) = - [ pe(35ft) – pe(50ft]

ke(50ft) = 0 since the brick is initially at rest

ke(35ft) = 340j - 2.27kg (9.81 m/s^2) (35ft)

(1m/3.28 ft)

ke(35ft)

= 102.38 j