When fighting fires, a firefighter must use great caution to hold a hose that emits large amounts of water at high speeds. Why would such a task be difficult?

The temperature inside a supernova explosion is said to be 2.00×1013 K .      (a) What would the average velocity vrms of hydrogen atoms be?(b) What is unreasonable about this velocity? (c) Which premise or assumption is responsible?

The next four questions use this description.  Our Sun has a peak emission wavelength of about 500 nm and a radius of about 700,000 km. Your dark-adapted eye has a pupil diameter of about 7 mm and can detect light intensity down to about 1.5 x 10-11 W/m2.  Assume the emissivity of the Sun is equal to 1. First, given these numbers, what is the surface temperature of the Sun in Kelvin to 3 significant digits? What is the power output of the Sun in moles of watts?  (in other words, take the number of watts and divide it by Avogadro's number) Assuming that all of the Sun's power is given off as 500 nm photons*, how many photons are given off by the Sun every second? Report your answer to the nearest power of 10 (e.g. if you got 7 x 1024, give your answer as 25).

How much heat is needed to raise the temperature of 0.200 kg of water from 20 oC to 100 oC? Note that the specific heat of water is 4200 J/(kg oC).

If a mercury thermometer is immersed in hot liquid, the mercury level goes down at first and then goes up. Explain why this happens.

The radiant flux at Earth is 1365 W/m2. Say we move towards the sun to a radius that is 1/3 the radius of the Earth's orbit. By what factor would the radiant flux increase or decrease?

Calculate the amount of radiation emitted for a unit surface (1 m²) for the following situations. Express your answers in both SI units (in W) and U.S. Customary units (in Btu/h). (a) a hot pavement in Arizona at 52°C (125.6°F) and & ≈ 0.84 rate in W rate in Btu/h W Btu/h (b) a hood of a car at 44°C (111.2°F) and & ≈ 0.91 rate in W W rate in Btu/h Btu/h (c) a sunbather at 38°C (100.4°F) and & ≈ 0.91 rate in W W rate in Btu/h Btu/h