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**1. Homework Statement**

A star-wars laser satellite, whose mass is 5000 kg, is orbiting Earth at a speed of 10.0 km/s. It launches a photon torpedo at an enemy missile which is directly in front of it. The photon torpedo contains [tex]10^3^3[/tex] photons, each having a wavelength of 200nm. What is the speed of the weapons satellite just after the launch?

**2. Homework Equations**

Conservation Of Momentum(?)(COM)

[tex]K_m_a_x = hf - \varphi[/tex]

[tex]KE = \gamma mc^2 - mc^2[/tex]

[tex]p = E/c[/tex]

[tex]v = f\lambda[/tex]

**3. The Attempt at a Solution**

Since we have [tex]\lambda = 200nm[/tex] we can then obtain f = 1.5*10^15 Hz.

However, from here on, i am lost. How do we use the number of photons and equate it in to [tex]p = E/c[/tex] and finally COM. And then there is also a problem of E which i am unable to find since i don't have h, [tex]K_m_a_x = hf - \varphi[/tex].

Any help will be appreciated. Thanks