How Many Photons Are Produced from a Falling Mass?

[NRip897]

Homework Statement

A 0.39 kg mass falls from a height of 2.9 m. If all of the energy of this mass could be converted to visible light of wavelength 5.5 × 10^−7 m, how many photons would be produced? The acceleration of gravity is 9.8 m/s^2 . Planck’s constant is 6.63 × 10^−34 J · s, and the speed of light is 3 × 10^8 m/s.

Homework Equations

E=hc/λ
p=h/λ
x=.5at^2

The Attempt at a Solution

E=hc/λ=(1.99x10^-25)/(5.5x10^-7)=3.618x10^-10J
x=.5at^2 > 2.9=.5(9.8)t^2 > t=.769s

 

[Mark Mendl]

Homework Statement

A 0.39 kg mass falls from a height of 2.9 m. If all of the energy of this mass could be converted to visible light of wavelength 5.5 × 10^−7 m, how many photons would be produced? The acceleration of gravity is 9.8 m/s^2 . Planck’s constant is 6.63 × 10^−34 J · s, and the speed of light is 3 × 10^8 m/s.

Homework Equations

E=hc/λ
p=h/λ
x=.5at^2

The Attempt at a Solution

E=hc/λ=(1.99x10^-25)/(5.5x10^-7)=3.618x10^-10J
x=.5at^2 > 2.9=.5(9.8)t^2 > t=.769s

Well, I think you can just calculate the initial energy E=mgh, assuming it was at rest before the fall.
You already have the energy of one photon E_photon=hc/λ, so the number of photons will be just E/E_photon