# Special Relativity Energy Problem a little confused!

1. Sep 18, 2012

### Engineergirl2

1. The problem statement, all variables and given/known data
At Earth's location, the intensity of sunlight is 1.5kW/m^2. if no energy escaped earth, by how much would Earth's mass increase in 1 day?

2. Relevant equations
ΔE=Δmc^2+ΔKE
Rearth=6.378x10^3

3. The attempt at a solution
I know that the change in kinetic energy does not change, so that value can go to 0. But I'm not sure what exactly I'm supposed to start with. The answer is supposed to be 1.83x10^5kg/day. Any help would REALLY be appreciated.

2. Sep 18, 2012

### nasu

You need to calculate how much energy is received in 1 day by the entire Earth.
You know how much is received in one second (kW is energy per second) by 1 m^2 of the surface.

3. Sep 18, 2012

### Engineergirl2

Do I use cross sectional area?

4. Sep 18, 2012

### nasu

You can use the cross sectional area and assume the radiation is normal on it.
Integrating over the area of the (hemi-)sphere and taking into account the angle of incidence for each location will produce the same result.