Solving Density ρ Question: Δρ = -87x10-6ρ at 25ºC to -40ºC

[A_Munk3y]

Homework Statement

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?

Homework Equations

βLead= 87x10^-6

The Attempt at a Solution

ok i already go the first part, but i don't think I am 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 that's 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 :)