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Is this right? (base units question)

Prove the base units of intensity are kgs^-3 When I= P/4(pi)r^2

So i did power = force x veloctiy and since force = ma this gives
kgms^-2 x ms^-1 = kgm^2 s^-3
r^2 = m^2
So kgm^2 s^-3 / m^2 = kgs^-3

Is that right? im missing the mark schemes for phy 3 (edexcel) june 2005 otherwise i could have checked it against that but just need some clarification. cheers.

Also i have some good definitions for bilogical and radioactive half life but how would you define in words the effective half life. I mean i know what it is but could you say it is the sum of the biological and radioactive half lives combined??

Reply 1

Eau

Looks alright to me (the units).

Effective half life = half life

Reply 2

iceman_jondoe

are you sure? (about the effective half life?)

Reply 3

Eau

iceman_jondoe

are you sure? (about the effective half life?)

No... lol.

Here's an alternative definition:

"The half-life of a radioisotope in a biological organism, resulting from a combination of radioactive decay and biological elimination."