density ρ question.

[A_Munk3y]

1. The problem statement, all variables and given/known data
Show that the change in the density ρ of a substance, when the temperature changes by ΔT,
is given by Δρ = −βρ ΔT. (b) What is the fractional change in density of a lead sphere whose
temperature decreases from 25°C to −40º C?


2. Relevant equations
βLead= 87x10-6

3. The attempt at a solution
ok i already go the first part, but i dont think im doing b right.

im just plugging in (-40-25) for temperature, and the β of lead.
so Δρ = −87x10-6ρ
ρ=176.8Δρ

i doubt thats the answer. am i misunderstanding the question here? or am i just doing something completely wrong?

[ideasrule]

ρ=176.8Δρ


This is right, but the question asks for fractional change in density. That means the change in density divided by the density itself.

[A_Munk3y]

oh... ok
thank you :)